bitwise operations on registers

[Andrew Cagney]

> 
> Can't really do this, but you can at least:
> define current
> ((struct task_struct *)($esp & ~8191))
> end
> 
> (gdb) current
> $33 = <blah>
> (gdb) $33->pid

You've also got:
	(gdb) set $current = ($esp & ~8191)
but that is only evaluated once (If I remember right).

The next step would be to add it to the stop-hook so it is executed 
after every stop.

Andrew