LearnBoost/socket.io — pull request #588 by tbranyen (2011-10-20 16:52:22+00:00)
Title: normalize the upgrade header to lowercase for ie 10 compatibility

Just started using IE 10's WebSocket implementation and noticed the upgrade header they send does not match the case tested for in the `hybi-07-12.js` source.

This simple patch allows WebSockets to be used successfully in the latest IE 10 developer preview.