Add initial support for taking listeners through handoff

* Core: Fix handle close callbacks that weren't ever getting fired
* Master: Fix keys for rewind buffer send... Typo was causing buffer to get
  assigned to the wrong stream
* SourceIn: Asking winston to log the listen spec was crashing when it was
  a handle
* Outputs: create `@client` object, refine handling
* Slave: Add support for listener handoff
* Slave.Stream: Use client object from output

* FIXME: Icecast output isn't working correctly on a handoff because we aren't
  checking to make sure that the metadata injection is keeping the same offset
  in the data.  Need to figure out a way to flush the Icecast writer before
  handing off or bringing state along for the new writer.