Added httplib2 support. (Working)

I added support for httplib2 with test code. I fixed the problems with the outgoing connections.

I changed `VCRHTTPSConnection` and `VCRHTTPConnection` "__init__" methods to perform some checking of the kwargs passed to the parent class and to set some attributes needed by httplib2's (ca_certs, proxy_info, etc). It's pretty ugly, but I don't know how to do it other way.