The Dialer.Dial method returns an *http.Response on a bad handshake.
This CL updates the Dial method to include up to 1024 bytes of the
response body in the returned *http.Response. Applications may find the
response body helpful when debugging bad handshakes.
Fixes issue #62.
Update the default origin test to treat no origin specified as OK. If
the client can create a request without the origin set, then the client
can also create a request with an arbitrary origin.