code review for transport patch

[Nathan Mittler]

Hey guys,
I took a crack at a fix which sends a stomp error frame back to the client in the event of a failure during authentication or authorization.  I haven't been through much of this code before, so I'd like to get some feedback on my changes.

Part of my concern is that some of the tweaks will affect all protocols (not only stomp) so I want to make sure I get it right.  In particular, a connection error is returned back to the client if an exception is caught by the TransportConnection.onCommand.  In the case of stomp, this ends up as a stomp error frame.

Here's the patch against the latest trunk:

http://people.apache.org/~nmittler/patch.txt

I also have a tarball if anyone wants to check it out:

http://people.apache.org/~nmittler/apache-activemq-4.2-incubator-SNAPSHOT.tar.gz

Thanks,
Nate