3.0 Rewrite HttpSocket

A few weeks ago I posted to the cakephp-core maling list that I felt the current HttpSocket object could use some love.  I wrote up some [documentation](https://github.com/markstory/cakephp/wiki/Httpsocket-improvements) for how I thought things should work.

I've implemented all features/API described in that wiki page.  There is still some re-factoring that could be done to better share code with `Network\Response` and `Network\Request`. Additionally there is an opportunity to re-use the Multipart message code in `Network\Email\Email`.  I've not done those yet but will do them in future pull requests. Once people are happy with this, I'll finish off the docs and update the upgradeshell.