[ssl] small cleanup

On Windows, errno.EWOULDBLOCK == errno.WSAEWOULDBLOCK
[jsonrpc] move tracing responsiblity to client

If clients want to implement logging of every packet, they have to implement
their own _log_request / _log_response methods. Client can do this in a more
meaningful way.
[setup] a workaround to install cffi automatically

Nice hack or too clever to be worth it?