use tunnel.sock instead of resp.fp in SSLTunnelConnection

resp.fp is a socket._fileobject instead of a socket.socket object,
so it is incompatible with gevent.
Fix issue #163
add test for SSLTunnelConnection
Merge pull request #157 from Infinidat/pull_request_2

Fix SSL tunnel socket
fix httplib NameError
add test
Merge pull request #156 from Infinidat/pull_request_1

fix httplib NameError
white space consistency

tab length is 3 spaces, except for the code in ReadDocument
Merge pull request #167 from Infinidat/pull_request_5

white space consistency