[1.2.X] Fixed #12407 - Document 'call_command' - thanks UloPe for the...

[1.2.X] Fixed #12407 - Document 'call_command' - thanks UloPe for the suggestion and adamv for the patch.

Backport of r14818 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14819 bcc190cf-cafb-0310-a4f2-bffc1f526a37