- Concatenate 'accept', 'accept-charset', 'accept-encoding',
  'accept-language', 'connection', 'cookie', and 'x-*' headers.
- For all others, drop duplicates.

Note that * in the .out files is a special wildcard.

- Add a unit test for client HTTP upgrade.
- Move around unit tests for server HTTP upgrade.

And add a few more tests.

Instead of just decoding Utf8, this will proxy requests to buffer.toString()
for other encodings. This makes for a simpler interface.

- Without this, recvMsg can be invoked before the event emitter gets a
  chance to run. In this case, recvMsg.fd will be overwritten and the
  original caller can end up emitting null.

Add callback param to listen() instead