This commit mirrors work done in the commit for ClsInsts, 5efe9b...

Specifically:
- All FamInsts have *fresh* type variables. So, no more freshness work
in addLocalFamInst

Also:
- Some pretty-printing code around FamInsts was cleaned up a bit
This caused location information to be added to CoAxioms and index
information to be added to FamInstBranches.