[1.1.X] Fixed #12001 -- Modified the example of form validation to use the...

[1.1.X] Fixed #12001 -- Modified the example of form validation to use the form's error class, rather than assuming ErrorList. Thanks to Suor for the report, and timo for the patch.

Backport of r13221 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@13226 bcc190cf-cafb-0310-a4f2-bffc1f526a37