Fixed #9964 -- Ensure that all database operations make transactions dirty, not just write operations. Many thanks to Shai Berger for his work and persistence on this issue.

This is BACKWARDS INCOMPATIBLE for anyone relying on the current behavior that allows manually managed read-only transactions to be left dangling without a manual commit or rollback.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15493 bcc190cf-cafb-0310-a4f2-bffc1f526a37