Browser request timeout broken

Hi, AJ!

I know you're off to bigger and better things, but I recently kludged this into working.

XHR2 appears to have its own timeout mechanism, but when I tried (only once) to use
it, it didn't do anything. This makes it so that setting options.timeout actually aborts the
request, though I didn't do anything special to prevent both 'abort' and 'timeout' from
being emitted.