Handshake should be synchronous

[davidchappelle]

The capabilities handshake that is performed at the start of a session should be a synchronous operation or at least return a future that can be waited upon so that you can be prevented from trying to join a session before the handshake has completed. We must ensure that the wamp router that we are connecting to can even support our capabilities before trying to establish a session. Based on the current coding style the future returned by a call to start a session should look as follows:

boost::promise<bool> m_handshake;

inline
boost::future<bool> start();

I will write-up a patch for review.

[davidchappelle]

This is fixed in my fork: Implemented in my fork: https://github.com/davidchappelle/AutobahnCpp