When a stream is opened we are searching for the best (currently) available channel.
The stream will then be keept on that channel.
Adjusted the rest of the algorithms that they now respect this rule.
improved a HashMap for Pids to be based on a Vec. Also using this for Sid -> Cid relation which is more performance critical
WARN: our current send()? error handling allows it for some close_stream messages to get lost.
