job control stuff in tracepoint.c

[Mark Kettenis <kettenis@wins.uva.nl>]

Ok, I'm looking into cleaning up some host-dependent stuff;
autoconfigifying bits and so on.

I'm currently looking into stuff dealing with job-control signals
(SIGTSTP. sigprocmask, sigsetmask).  In that context we also do some
really wierd stuff with a macro called STOP_SIGNAL.  The reason for
its existence has been eliminated (broken job-control handling on the
Convex, support for which has been removed), yet it still exists.  I'd
like to eleminate STOP_SIGNAL (and revert to using SIGTSTP where
appropriate), but when I did that I discovered that STOP_SIGNAL is
used in tracepoint.c wheras it isn't defined at all, not even to
SIGTSTP.  Replacing #ifdef STOP_SIGNAL, with #ifdef SIGTSTP leads to
compilation failure since the variable job_control isn't declared.

I'm not quite sure what the code is trying to do.  Something with
redisplaying the prompt when running asynchronously?  Elena, can you
shed some light on this?

Mark