pn_connector makes a blocking call to socket::connect

The proton-c driver makes a blocking call to 'connect' when establishing outgoing connections via pn_connector. This breaks the asynchronous nature of the proton driver which should block only on pn_driver_wait.

To work properly, pn_connector should return immediately and the connector should then appear in the driver's work list later when the transport connection is either successfully established or it fails for some reason.