Cleanup ist_resume and ist_recurse, notes below.

Concerning doreti:
Old code was doing:
cli
make sure ipendings are cleared
continue

I'm not totally sure the ipending test is required, but I've kept the
same behaviour.
Remote is_recurse and is_resume.
Remove ci_ilevel, also cleanup the wankery of labels on doreti.
Remove iunmask and mask from cpu_info{}.
More love to doreti, remove the remaining leftovers.
Fix the stack for clock interrupts, fixes the bug where everything was
being accounted as systime, I need to think up a better fix for it.