Merged gevent/zmq updates, ported to requests >= 1.2

For a clean diff ignore whitespaces: https://github.com/EnTeQuAk/locust/compare/locust_0_7_changes?expand=1&w=1

I reverted the big whitespace changes but left "usual stuff" that were in all the commits where I actually touched the code. Hope this is fine enough.

Cheers,
Chris