[Stackless] priority patch

[Andrew Francis]

Hello Kristjan:

>If no one objects too strongly to this I'm hoping to get this accepted >into the trunk.

I would have to examine your algorithm in more detail. This takes
time. I have been reviewing your StacklessIO EVE-Online stuff.
I have being going over scheduling algorithms in general. And 
reading the Pike and Cardelli works on rendezvous communications. 

Gut reaction: I am not sure if tasklet priority and rendezvous 
semantics mix well. Also, when I see tasklet priority, the first 
thing I look at is whether starvation could occur.

That said, I would recommend that you test these ideas out in PyPy.
PyPy will be the place I will test new algorithms and feature.

As for the trunk. It is your show. I guess if I feel uncomfortable with tasklet priority, I won't use it.

Cheers,
Andrew