throw Errors from mapTyVars such that Bare can catch them
fix another crash due to calling toType on an RType containing holes
better error location
use GHC tyvars for plugged dataconp
renameTyVars is subsumed by plugHoles
mapTyVars in abs-refs too
hole-crash2.hs should be in tests/crash
Merge pull request #239 from gridaphobe/fix-more-holes

Fix more crashes due to holes.

fixes #238