better scheduler with correct sleep times

[Scott David Daniels]

sokol wrote:
> ...
> 
> I see what you did there. You are keeping the queue empty
> so you get notified for free, while I introduced a new
> threading Condition to detect insertions.
> All that is missing in your version is to put back all
> pending tasks when somebody sends the stop (None) request.
> 
> Shouldn't sched module do something similar?

Probably so, I was just scratching an itch that I had.
My target was to make the decisions as clear as possible.
What I started from is "you only need to do work when
the next thing comes up or another entry is added."

That was the core I was going after, and I just had the None
in there so my tests could stop gracefully (in fact I printed
the leftover queue when I was testing).

--Scott David Daniels
Scott.Daniels at Acm.Org