[1.0.X] Fixed #10450 -- Fixed an initialisation problem in the savepoint code.

Patch from Jeremy Dunck.

Backport of r10511 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10512 bcc190cf-cafb-0310-a4f2-bffc1f526a37