Clarify which tests to run in the Makefile

If you put your Virtualenv in the same folder as Requests (as I
usually do), py.test will pick up any test_* files inside the
virtualenv and attempt to run them too, leading to the following error:
https://gist.github.com/kevinburke/1aa2b07e01de3a7daa15

Instead specify the test file we would like to run in the Makefile.
clarify comment
Add support for connect timeouts

Modifies the timeout interface to also accept a tuple (connect, read) which
would be used to set individual connect and read timeouts for Requests. Adds
Advanced documentation explaining the interface and providing guidance for
timeout values.
revert change
ConnectTimeout multiple inheritance
assert connect timeout inheritance
woops
Updates urllib3 to 528ad3c

This includes fixes for openssl running with Pypy, so SSL connections can be
made if ndg-httpsclient, pyopenssl and pyasn1 are installed.

see also:

- https://github.com/shazow/urllib3/issues/449
- https://github.com/pypa/pip/issues/1988
Merge pull request #2179 from kevinburke/urllib3-pypy-ssl

Updates urllib3 to 528ad3c
Merge pull request #2176 from kevinburke/connect

Add support for connect timeouts
Merge pull request #2174 from kevinburke/test-clarification

Clarify which tests to run in the Makefile
Add Session method to merge environment settings with per-request settings
Update verify check and doc-string