gdbstub initial code, v4

[Oleg Nesterov <oleg at redhat dot com>]

Changes:

	Only internal cleanups. I was busy with utrace fixes
	and testing.

With utrace patches I sent, I do not see any problems so far.
But utrace definitely needs more changes.

Next step: handle exit correctly and report W/S. I misunderstood
what gdbserver does when the main thread exits, it is not stupid
as I wrongly thought.

Note the second attachment, GDBCAT. It is just the simple perl
script which connects /proc/ugdb to tcp port. It can be used for
remote debugging via tcp, or with (unpatched) gdb which can't do
select() on /proc/ugdb. Actually, it is more convenient to use
it in any case, at least for logging purposes.

Oleg.

Attachment: ugdb.c
Description: Text document

Attachment: GDBCAT
Description: Text document