Comparison primops return Int# (Fixes #6135)

This patch modifies all comparison primops for Char#, Int#, Word#, Double#,
Float# and Addr# to return Int# instead of Bool. A value of 1# represents True
and 0# represents False. For a more detailed description of motivation for this
change, discussion of implementation details and benchmarking results please
visit the wiki page: http://hackage.haskell.org/trac/ghc/wiki/PrimBool

There's also some cleanup: whitespace fixes in files that were extensively edited
in this patch and constant folding rules for Integer div and mod operators (which
for some reason have been left out up till now).