[1.2.X] Fixed #14728 -- Broadened warning about django-admin.py missing .py...

[1.2.X] Fixed #14728 -- Broadened warning about django-admin.py missing .py suffix to include more than just Ubuntu, since at least Fedora also does this. Thanks to giallu for the report.

Backport of r14621 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14622 bcc190cf-cafb-0310-a4f2-bffc1f526a37