[project @ 1999-09-11 18:30:49 by sof]

Experimental support for re-routeing I/O on a Handle to that of another
for the duration of an IO action. Used to provide the following three
(exported) actions

   withStdin, withStdout, withStderr :: Handle -> IO a -> IO a

which 'replaces' one of the standard handles with that of the supplied
handle while performing the second action.