Reference PR for wrapping HTTP(S)Connection and disabling Nagle by default

This is a broken branch for now, but wanted to share my (little) progress...

Related to #253 and the discussion in #254. 

Outstanding issues:
- [ ] Can't inherit from httplib classes and use super(...) because they're old-style classes.
- [ ] I'd like to reduce repeating logic by reusing it in `_new_conn` and `_prepare_conn`. This is half-done.
- [ ] Consider whether we want to vendor in more of httplib/http.client logic into urllib3. Or maybe roll our own? Doesn't seem like that much... #famouslastwords (cc @lukasa)
  - If we do roll our own, we can put it inside `urllib3.yolo`. #halfjoking
- [ ] Allow some kind of backwards compat access to `source_address` (Py26 sockets don't have it).
- ...

Anyone interested in picking this up?