tc: allow to coerce `b:bool{phi}` to Type, too
tc: allow to coerce `b:bool{phi}` to Type, too

This needs to be in place for the #57 fix, since we introduce the
refinement in many places.

A-Manning/FStar,A-Manning/FStar,FStarLang/FStar,FStarLang/FStar,A-Manning/FStar,FStarLang/FStar