It turns out that we need to treat filename creation/display (in
particular, the upload_to path) differently depending upon whether the value is
out of the database or provided by other code and there's no reliable way to
determine that at the moment (although some later proposed changes might alter
that). So calling get_FIELD_filename on an unsaved model with a changed file
attribute will not necessarily return the same result as after the save().

Refs #5619. Fixed #7843.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7998 bcc190cf-cafb-0310-a4f2-bffc1f526a37