Consider patching Radio.Channel instead of Radio.channel

[cmaher]

As per some discussion over in marionettejs/backbone.radio#136 (comment), it is a perfectly valid use-case to do new Radio.Channel, which does not expose the channel on the global _channels (really want some weak references in my life). We should consider patching the constructor to get a hold of all channels.

[jasonLaster]

Yep