Add status ping from master to slave

* Update coffeescript to 1.7.1
* Update Underscore to 1.6.0
* Update Socket.io to 1.0.5
* Slave: Add socket listener for `status`.  When called, return an object containing
  metrics about stream rewind buffers.
* Master: Don't consider a slave to be connected until it sends us an `ok` event. Cuts
  down on phantom slaves during startup and transport negotiation.
* Master: Ping slave `status` endpoints every five seconds
* RewindBuffer: Add `_rStatus` function
* HLSSegmenter: Add `status` function
* Downgrade some noisy logging messages