remove a bit more stuff in 'make clean'.
remove a bit more stuff in 'make clean'.

We can't use Cabal to clean up, because it stops working when things
are removed.

FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs