types were supposed to be identical but only needed to be
compatible.  This gets rid of the Type.literal method.  I
renamed the Type.rep method to Type.lit because I believe it
corresponds to the term "literal" as used in the spec.

R=rsc
APPROVED=rsc
DELTA=228  (57 added, 35 deleted, 136 changed)
OCL=32606
CL=32608