http: improves expect header handling

Now returns a 417 error status or allows for an event listener on
the `checkExpectation` event. Before we were ignoring requests that
had misspelled `100-continue` values for expect headers.

This is a quick port of the work done here:
https://github.com/nodejs/node-v0.x-archive/pull/7132 by alFReD-NSH
with surrounding discussion here:
https://github.com/nodejs/node-v0.x-archive/issues/4651

Also updates all the instances of the deprecated
EventEmitter.listenerCount to the current self.listenerCount. Most
of these were in the new code ported over but there was another
legacy instance.

Refs: #2403
PR-URL: https://github.com/nodejs/node/pull/4501


Reviewed-By: James M Snell <jasnell@gmail.com>