[1.2.X] Fixed #15364 -- Ensure files are closed correctly during file tests....

[1.2.X] Fixed #15364 -- Ensure files are closed correctly during file tests. Thanks to Mila for the report and patch.

Backport of r15604 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15608 bcc190cf-cafb-0310-a4f2-bffc1f526a37