Added django.template.Token.split_contents() and used it to add support for...

Added django.template.Token.split_contents() and used it to add support for strings with spaces in {% ifchanged %}

git-svn-id: http://code.djangoproject.com/svn/django/trunk@3112 bcc190cf-cafb-0310-a4f2-bffc1f526a37