vms Meta key hack (trunk only)

vms Meta key hack (trunk only)

     I can't figure out how to make PuTTY use the Alt key to function as
a Meta key and set a character's high bit, so I used this hack to test
the M-5 fix just committed.  This lets me specify a character to be used
to force the next character to have its high bit set, so I can fake the
Meta key with a two character sequence.  (I used the back-tick/accent,
since nethack doesn't do anything special with it.)  Conceivably something
like this should be promoted to the core; this just affects VMS, and only
when vmstty.c is compiled with DEBUG defined.