clean up GossipSender and make it more self-contained
clean up GossipSender and make it more self-contained

In particular don't require Send() to be serialised by the caller.

We split up the triple(!) purpose 'cell' channel into:

1) a 'cell' member, holding pending GossipData or nil
2) a 'more' channel, for signalling that 'cell' has been filled
3) a 'stop' channel, for requesting termination

rade/weave,weaveworks/weave,dpw/weave,n054/weave,rade/weave,tomwilkie/weave,paulbellamy/weave,tomwilkie/weave,n054/weave,tomwilkie/weave,tomwilkie/weave,n054/weave,n054/weave,dpw/weave,weaveworks/weave,dpw/weave,rade/weave,tomwilkie/weave,dpw/weave,paulbellamy/weave,rade/weave,weaveworks/weave,paulbellamy/weave,dpw/weave,n054/weave,paulbellamy/weave,weaveworks/weave,rade/weave