Revert some of the UTF8 changes, use UTF8 only for files we know are UTF8

So we use ordinary read/writeFile for ordinary text files. For console
output we use ordinary putStr etc and we'll just hope that haskell
implementations catch up and deal with that sensibly. Don't assume
captured program output is UTF8, use the default encoding.
So we use binary mode IO along with UTF8 encoding and decoding only for 
file types that we specify to be UTF8, which are .cabal files and
.hs/.lhs files only.