[1.2.X] Fixed #14158 -- Fixed SelectMultiple._has_changed to not assume same...

[1.2.X] Fixed #14158 -- Fixed SelectMultiple._has_changed to not assume same order of data anymore. Thanks, akaariai and dmoisset.

Backport from trunk (r14887).

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14907 bcc190cf-cafb-0310-a4f2-bffc1f526a37