issue #979 RaceCondition Nailed

@zacronos @kandizzy @gitnik @cthrax 
I will get to commenting on the PR in a few minutes. This is 3 days worth of work and a whole Sunday of thinking about it.

Everything is based of discussion and ideas @aesnyder and I had on canceling promises.

Seriously complicated PR, and I plan on doing a hangout with @aesnyder and with anyone who cares
maybeCanceled is our fallout mechanism which gets passed into _async.each. Where async.each will trip keepGoing to false when maybeCanceled is `'cancel safe'`