Fixed #12913. Fields with choices now respect show_hidden_initial as a keyword...

Fixed #12913. Fields with choices now respect show_hidden_initial as a keyword argument to formfield. Thanks, semenov.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12696 bcc190cf-cafb-0310-a4f2-bffc1f526a37