merge from stable revs:
  1.121.4.1 +7 -6      fptools/ghc/rts/GC.c
  1.9.4.1   +4 -1      fptools/ghc/rts/GCCompact.c
  1.17.4.1  +4 -3      fptools/ghc/rts/StoragePriv.h

  SimonM's fixes to deal with GHCi and CAFs properly in the compacting
  collector.