[jhc] darcs patch: properly check for duplicate instances (and 3 more)

Sat Feb 4 17:56:51 PST 2012 John Meacham <john@repetae.net> * properly check for duplicate instances Sat Feb 4 18:58:15 PST 2012 John Meacham <john@repetae.net> * check superclass constraints on instance declarations Sun Feb 5 00:21:56 PST 2012 John Meacham <john@repetae.net> * fix up library to pass the more strigent typechecking Sun Feb 5 03:08:57 PST 2012 John Meacham <john@repetae.net> * generate reverse name map during renaming