[1.1.X] Fixed #11900 -- Corrected an edge case of transaction handling in the...

[1.1.X] Fixed #11900 -- Corrected an edge case of transaction handling in the commit_on_success decorator. Thanks to guettli for the report, and Gabriel Hurley for the initial test case.

Backport of r12764 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12765 bcc190cf-cafb-0310-a4f2-bffc1f526a37