[1.2.X] Fixed #13623 - code in intro-tutorial03 missing an import statement

Thanks to lescoutinhovr@gmail.com, AMJ for the report, and to zerok/timo for
the patch.

Backport of [13847] from trunk

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13848 bcc190cf-cafb-0310-a4f2-bffc1f526a37