catch exception in wamp_session::send_msg in case of problems with underlying socket

[uquendo]

Catching write exception on the session it belongs to instead of propagating further (for example, to pubsub_man::update_topic) and possibly dropping the session that posted the data to the topic our problematic client is subscribed to.

Problem was observed when one slow subscriber (able to hit wampcc::default_socket_max_pending_write_bytes limit) was able to drop the sessions of all the publishers to the topics it is subscribed to.

[darrenjs]

Hi, I need to review this in a bit more in depth, because the call to handle_exception(); is really only intended for inbound traffic. Although the send_msg is also used internally. I will try to reproduce your error.