Fixed #4948, a race condition in file saving. Thanks to Martin von Löwis, who...

Fixed #4948, a race condition in file saving. Thanks to Martin von Löwis, who diagnosed the problem and pointed the way to a fix.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8306 bcc190cf-cafb-0310-a4f2-bffc1f526a37