Use only subscriptionId for subscription matching

Based on [STOMP 1.2 spec](http://stomp.github.io/stomp-specification-1.2.html#MESSAGE), subscription matching should rely only on subscriptionId, not on subscriptionId + destination.

I hit this bug when using STOMP Dart client with a Spring 4.0.3 server with [@SubscribeMapping annotation](http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle/#websocket-stomp-handle-annotations). In the case the SUBSCRIBE destination is /app/aaaaaa and the MESSAGE destination received is /aaaaaa with matching subscriptionId. Based on STOMP 1.2 spec, I think Spring implementation is correct.

If you agree with this fix, could you release Stomp client 0.7.2 since I need this in my [OpenSnap](https://github.com/sdeleuze/opensnap) Spring + Dart SnapChat clone ?