I fixed up the 'remove thread group inferiors from the tasklist' patch. I
think i managed to find a reasonably good construct to iterate over all
threads:

	do_each_thread(g, p) {
		...
	} while_each_thread(g, p);

the only caveat with this is that the construct suggests a single-loop -
while it's two loops internally - and 'break' will not work. I added a
comment to sched.h that warns about this, but perhaps it would help more
to have naming that suggests two loops:

	for_each_process_do_each_thread(g, p) {
		...
	} while_each_thread(g, p);

but this looks a bit too long. I dont know. We might as well use it all
unrolled and no helper macros - although with the above construct it's
pretty straightforward to iterate over all threads in the system.