Add

	DriverPhases.haskellish_src_suffix :: String -> Bool
	DriverPhases.haskellish_src_file   :: String -> Bool

which return True for suffixes of Haskell source files only.  The
existing haskellish_suffix and haskellish_file return True also for
.raw_s and .hc files.

We use these instead of haskellish_file in Main.main when deciding
whether to preprocess a file.

Fixes: compilation of .raw_s files, and potential bugs with
compilation of .hc files.