Fixed #15364 -- Ensure files are closed correctly during file tests. Thanks to...

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

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15604 bcc190cf-cafb-0310-a4f2-bffc1f526a37