test/channel: a basic channel functionality tests
fix/channel: use err.code instead of err.errno
  since node sometimes gives err.errno as a string, and sometimes as a number
fix/channel/mp: left-out export, leading to incorrect error handling
channel/mp: debugify
channel: fix incorrect variable naming, that caused incorrect terminate handling
channel: move .close from .hdl.data to .hdl.message
  since .hdl.message has the right context for message form checking
channel: more or less uniform debug reporting of skipped messages
dependencies: add mocha and other development-time dependencies
channel: add comment for _injectSocket
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