Improved VectInfo

Improved VectInfo
- We need to keep pairs of (f, f_CC) in VectInfo as it is difficult
  to obtain Names from OccNames (of imported modules) in Core passes.
- There is a choice of keeping Names or Vars in VectInfo.  We go with Vars
  for now; mainly to avoid converting between Names and Vars repeatedly for
  the same VectInfo in other than one-shot mode.

  Again goes to the HEAD straight away to avoid conflicts down the road.