I added a few more text transform options:

• Added RubyPants support (auto-adds smart quotes and dashes). Uses filter string 'smartypants'.
• Changed HtmlEngine.transform to allow multiple transforms to be stacked ('markdown smartypants' will run the BlueCloth filter followed by the RubyPants filter).
• Added 'SmartyPants' and 'Markdown with Smartypants' options to Movable Type API and admin UI.
• Fixed filter_html in HtmlEngine.transform--before, it would only apply if you used the Textile filter, so Markdown and unfiltered users would be screwed if users post cross-site-scripting in comments.
• Added new config item: comment_text_filter. Uses existing text_filter_options list. If unset, then the comment renderer will fall back on configtext_filter.

I haven't added any tests to this for two reasons. First, I couldn't find a set of tests for the HtmlEngine code. Second, most of the DB tests fail horribly when running on PostgreSQL--the DB foreign keys in the schema file raise exceptions during a lot of delete operations.