E.g. when using GSSAPI, the username may be picked up from that used to kinit. This needs to be exposed to the application.
Connection::getAuthenticatedUsername() method added. To test, this should return the user used for kinit when connecting with GSSAPI.
Committed on trunk (r959461) and in release repo (http://mrg1.lab.bos.redhat.com/git/?p=qpid.git;a=commitdiff;h=8d55e9d8981053f2bf584ae446dfe404293f11c9).