Request::abort() not implemented

http://nodejs.org/api/http.html#http_request_abort

I ran across this when using [request](https://github.com/request/request)'s timeout option that uses abort() internally.

Start by locating the Request implementation in http-browserify and compare its available methods with the Node.js http.request documentation linked in the issue. Trace how request/request uses abort() for timeouts, then verify that the missing method is implemented and that the timeout path no longer fails.

Written by the indexing model from the issue text.