Comments and white space
Test Trac #9380
Add a fast-path in TcInteract.kickOutRewritable
Comments only
Add comments about the {-# INCOHERENT #-} for Typeable (f a)

C.f. Trac #9242
Complete work on new OVERLAPPABLE/OVERLAPPING pragmas (Trac #9242)

* Deprecate -XOverlappingInstances

* Update test suite.  Several tests even had entirely unnecessary
  uses of -XOverlappingInstances

* Update user manual with a careful description of the instance
  resolution story

* Fix an outright bug in the handling of duplidate instances in GHCi,
  which are meant to silently overwrite the earlier duplicate. The
  logic was right for family instances but was both more complicated,
  and plain wrong, for class instances.  (If you are interested, the
  bug was that we were eliminating the duplicate from the InstEnv, but
  not from the [ClsInst] held in tcg_insts.)  Test is ghci044a.