acu78070 - clearing sleep_timer

clearing sleep_timer when the sleep timer has finished
sleeping.
acu78070 - Fixed NB.yield to not call resume 

clearing sleep_timer when the sleep timer has finished
sleeping.
acu78070 - Added registration of reactor actions with their timeouts

Since many_ticks is used in the reactor for writers,
readers and yield, we need to handle these many_ticks
more similar in the way we handle handlers. Unfortunately,
we can't easily just cancel them. Currently, we use
flags to cancel them after a timeout fired. However, 
there is no guarantee that this flag hasn't been set
by a different call in the meanwhile. To solve these
issues, we register every scheduled reactor action
with its corresponding timeout.