Major Refactor of Stubs

So the stubs were getting out of hand, and while trying to add support for the
putrequest and putheader methods, I had an idea for a cleaner way to handle
the stubs using the VCRHTTPConnection more as a proxy object.  So
VCRHTTPConnection and VCRHTTPSConnection no longer inherit from HTTPConnection
and HTTPSConnection.  This allowed me to get rid of quite a bit of
copy-and-pasted stdlib code.
add tests for boto
httplib2 support
restore tox envs
Add httplib2 tests to travis
Cut down on the number of environments in Travis
Add Python 2.3 support

This commit also adds the 'six' dependency
Don't try to inherit from the real response object
urlencode moved in py3
let's add boto as a supported client, and maybe we dont need the empty travis env anymore
add more tox envs
fix self.closed in python3, and request must inherit from httprequest for httplib2
expose sock, pass correct args to connect in stubs.  should fix httplib2 in python3
need the sock for httplib2, don't want sock for requests, can't we all just get along?
add AWS keys to travis