Don't wake up threads when getting the next timer deadline.
If we are idling this can: remove thread from block list, get the
deadline for the next blocked thread, return to idle thread. This will
end up sleeping until the next wake up condition which in the worst
case would be rebalance, or indefinitely when not running SMP.
Make sure we always set the next timer deadline. I was not doing that if
the timer interrupt did not lead to a yield
Bananymous
0843b8989d