Fixed #17799 - Documented that the execute() method of a management command is not suitable for calling the command from code; call_command should be used instead. Thanks kacah222 for the report and claudep for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17629 bcc190cf-cafb-0310-a4f2-bffc1f526a37