Upgrade http-proxy and fix engine.io upgrades.

Pretty straightforward update to http-proxy v1.0.2 from v0.8.x notwithstanding the total overhaul:
https://github.com/nodejitsu/node-http-proxy/blob/master/UPGRADING.md

I was not able to track down what exactly was broken. In any event, this fixes it.

Tests pass (notwithstanding Travis). I'll add another test for the websockets, but I wanted to get this in front of you asap.