Inserting flow-control chars with an mpsafetty kernel

Hi Ed,

After installing the mpsafetty changes it seems that flow-control ^S and
^Q characters cannot be inserted inserted anymore.  I first noticed this
when CTRL-S stopped working as 'search-forward' in Emacs, but it seems
the same problem exists in /usr/bin/vi, vim, bash and a few other
programs that I tested.

With a kernel before the mpsafetty changes, I can fire up /usr/bin/vi
and type in insert-mode `^V^S'.  This correctly inserts a ^S character.
With a kernel from svn revision /head_at_181939 ^V no longer quotes the
next byte in vi(1) and other programs.