Fixed #17260 -- Added time zone aware aggregation and lookups.

Thanks Carl Meyer for the review.

Squashed commit of the following:

commit 4f290bdb60b7d8534abf4ca901bd0844612dcbda
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Wed Feb 13 21:21:30 2013 +0100

    Used '0:00' instead of 'UTC' which doesn't always exist in Oracle.

    Thanks Ian Kelly for the suggestion.

commit 01b6366f3ce67d57a58ca8f25e5be77911748638
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Wed Feb 13 13:38:43 2013 +0100

    Made tzname a parameter of datetime_extract/trunc_sql.

    This is required to work around a bug in Oracle.

commit 924a144ef8a80ba4daeeafbe9efaa826566e9d02
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Wed Feb 13 14:47:44 2013 +0100

    Added support for parameters in SELECT clauses.

commit b4351d2890cd1090d3ff2d203fe148937324c935
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Mon Feb 11 22:30:22 2013 +0100

    Documented backwards incompatibilities in the two previous commits.

commit 91ef84713c81bd455f559dacf790e586d08cacb9
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Mon Feb 11 09:42:31 2013 +0100

    Used QuerySet.datetimes for the admin's date_hierarchy.

commit 0d0de288a5210fa106cd4350961eb2006535cc5c
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Mon Feb 11 09:29:38 2013 +0100

    Used QuerySet.datetimes in date-based generic views.

commit 9c0859ff7c0b00734afe7fc15609d43d83215072
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Feb 10 21:43:25 2013 +0100

    Implemented QuerySet.datetimes on Oracle.

commit 68ab511a4ffbd2b811bf5da174d47e4dd90f28fc
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Feb 10 21:43:14 2013 +0100

    Implemented QuerySet.datetimes on MySQL.

commit 22d52681d347a8cdf568dc31ed032cbc61d049ef
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Feb 10 21:42:29 2013 +0100

    Implemented QuerySet.datetimes on SQLite.

commit f6800fd04c93722b45f9236976389e0b2fe436f5
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Feb 10 21:43:03 2013 +0100

    Implemented QuerySet.datetimes on PostgreSQL.

commit 0c829c23f4cf4d6804cadcc93032dd4c26b8c65e
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Feb 10 21:41:08 2013 +0100

    Added datetime-handling infrastructure in the ORM layers.

commit 104d82a7778cf3f0f5d03dfa53709c26df45daad
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Mon Feb 11 10:05:55 2013 +0100

    Updated null_queries tests to avoid clashing with the __second lookup.

commit c01bbb32358201b3ac8cb4291ef87b7612a2b8e6
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Feb 10 23:07:41 2013 +0100

    Updated tests of .dates().

    Replaced .dates() by .datetimes() for DateTimeFields.
    Replaced dates with datetimes in the expected output for DateFields.

commit 50fb7a52462fecf0127b38e7f3df322aeb287c43
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Feb 10 21:40:09 2013 +0100

    Updated and added tests for QuerySet.datetimes.

commit a8451a5004c437190e264667b1e6fb8acc3c1eeb
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Feb 10 22:34:46 2013 +0100

    Documented the new time lookups and updated the date lookups.

commit 29413eab2bd1d5e004598900c0dadc0521bbf4d3
Author: Aymeric Augustin <aymeric.augustin@m4x.org>
Date:   Sun Feb 10 16:15:49 2013 +0100

    Documented QuerySet.datetimes and updated QuerySet.dates.

1 files changed, 21 insertions, 13 deletions

diff --git a/django/db/models/sql/where.py b/django/db/models/sql/where.py
index cbb0546d6a..ef856893b5 100644
--- a/django/db/models/sql/where.py
+++ b/django/db/models/sql/where.py
@@ -8,11 +8,13 @@ import collections
 import datetime
 from itertools import repeat
 
-from django.utils import tree
-from django.db.models.fields import Field
+from django.conf import settings
+from django.db.models.fields import DateTimeField, Field
 from django.db.models.sql.datastructures import EmptyResultSet, Empty
 from django.db.models.sql.aggregates import Aggregate
 from django.utils.six.moves import xrange
+from django.utils import timezone
+from django.utils import tree
 
 # Connection types
 AND = 'AND'
@@ -60,7 +62,8 @@ class WhereNode(tree.Node):
         # about the value(s) to the query construction. Specifically, datetime
         # and empty values need special handling. Other types could be used
         # here in the future (using Python types is suggested for consistency).
-        if isinstance(value, datetime.datetime):
+        if (isinstance(value, datetime.datetime)
+            or (isinstance(obj.field, DateTimeField) and lookup_type != 'isnull')):
             value_annotation = datetime.datetime
         elif hasattr(value, 'value_annotation'):
             value_annotation = value.value_annotation
@@ -169,15 +172,13 @@ class WhereNode(tree.Node):
 
         if isinstance(lvalue, tuple):
             # A direct database column lookup.
-            field_sql = self.sql_for_columns(lvalue, qn, connection)
+            field_sql, field_params = self.sql_for_columns(lvalue, qn, connection), []
         else:
             # A smart object with an as_sql() method.
-            field_sql = lvalue.as_sql(qn, connection)
+            field_sql, field_params = lvalue.as_sql(qn, connection)
 
-        if value_annotation is datetime.datetime:
-            cast_sql = connection.ops.datetime_cast_sql()
-        else:
-            cast_sql = '%s'
+        is_datetime_field = value_annotation is datetime.datetime
+        cast_sql = connection.ops.datetime_cast_sql() if is_datetime_field else '%s'
 
         if hasattr(params, 'as_sql'):
             extra, params = params.as_sql(qn, connection)
@@ -185,6 +186,8 @@ class WhereNode(tree.Node):
         else:
             extra = ''
 
+        params = field_params + params
+
         if (len(params) == 1 and params[0] == '' and lookup_type == 'exact'
             and connection.features.interprets_empty_strings_as_nulls):
             lookup_type = 'isnull'
@@ -221,9 +224,14 @@ class WhereNode(tree.Node):
                         params)
         elif lookup_type in ('range', 'year'):
             return ('%s BETWEEN %%s and %%s' % field_sql, params)
+        elif is_datetime_field and lookup_type in ('month', 'day', 'week_day',
+                                                   'hour', 'minute', 'second'):
+            tzname = timezone.get_current_timezone_name() if settings.USE_TZ else None
+            sql, tz_params = connection.ops.datetime_extract_sql(lookup_type, field_sql, tzname)
+            return ('%s = %%s' % sql, tz_params + params)
         elif lookup_type in ('month', 'day', 'week_day'):
-            return ('%s = %%s' % connection.ops.date_extract_sql(lookup_type, field_sql),
-                    params)
+            return ('%s = %%s'
+                    % connection.ops.date_extract_sql(lookup_type, field_sql), params)
         elif lookup_type == 'isnull':
             assert value_annotation in (True, False), "Invalid value_annotation for isnull"
             return ('%s IS %sNULL' % (field_sql, ('' if value_annotation else 'NOT ')), ())
@@ -238,7 +246,7 @@ class WhereNode(tree.Node):
         """
         Returns the SQL fragment used for the left-hand side of a column
         constraint (for example, the "T1.foo" portion in the clause
-        "WHERE ... T1.foo = 6").
+        "WHERE ... T1.foo = 6") and a list of parameters.
         """
         table_alias, name, db_type = data
         if table_alias:
@@ -331,7 +339,7 @@ class ExtraWhere(object):
 
     def as_sql(self, qn=None, connection=None):
         sqls = ["(%s)" % sql for sql in self.sqls]
-        return " AND ".join(sqls), tuple(self.params or ())
+        return " AND ".join(sqls), list(self.params or ())
 
     def clone(self):
         return self