Fix arguments for unbound binders in RULE application
Fix arguments for unbound binders in RULE application

We were failing to correctly implement Note [Unbound RULE binders]
in Rules.hs.  In particular, when cooking up a fake Refl,
were were failing to apply the substitition.

This patch fixes that problem, and simultaneously tidies
up the impedence mis-match between RuleSubst and TCvSubst.

Thanks to Sebastian!

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc