Added datetime-handling infrastructure in the ORM layers.
Added datetime-handling infrastructure for the GIS backends.
Implemented QuerySet.datetimes on PostgreSQL.
Implemented QuerySet.datetimes on SQLite.
Implemented QuerySet.datetimes on MySQL.
Implemented QuerySet.datetimes on Oracle.
Used QuerySet.datetimes in date-based generic views.
Used QuerySet.datetimes for the admin's date_hierarchy.