waylan/Python-Markdown — pull request #122 by Scorpil (2012-07-19 22:06:56+00:00)
Title: More expressive ValueError description on adding nonexistent middleware

Old error message:
ValueError: list.index(x): x not in list

New error message:
ValueError: Element 'extension' was not found in OrderedDict

Sorry for mess with commits... Had a typo there. ;)