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Naming:
  I also considered urlparse2 (ala urllib2) but liked having
a name without a version number attached.  rfc3986 would
also work I suppose, but seems a bit... clunky.

MailtoURIParser:
  You seem to have missed the point (probably due to my poor
documentation): none of the *URIParser classes are meant to
be directly used; they're just the default population of an
extensible structure that URIParser uses to do the work of
parsing.  

Let's move discussion to python-dev.  I'll put
changed/fixed/upgraded versions here as I adjust them due to
feedback.  Here's the first (adjusted due to your feedback).