rewrote all <subst> code using <type_variable> instances rather than   an assoc of ints, including the 'path' compression suggested by the   secret eoplv1 draft chapter.  probably still some more cleaning up   to do.
rewrote all <subst> code using <type_variable> instances rather than
  an assoc of ints, including the 'path' compression suggested by the
  secret eoplv1 draft chapter.  probably still some more cleaning up
  to do.


git-svn-id: 6b0ac017e42d307e3c8dde35033ecb159d7d210f@23 6687424e-f796-406d-b1dd-24293e5947de

samrushing/irken-compiler,samrushing/irken-compiler,samrushing/irken-compiler,samrushing/irken-compiler