Fixed #8285: signal handlers that aren't functions work under DEBUG. This...

Fixed #8285: signal handlers that aren't functions work under DEBUG. This slightly loosens the sanity check, but things that are valid under production shouldn't fail under debug.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8546 bcc190cf-cafb-0310-a4f2-bffc1f526a37