PROTON-452: Expose the Messenger interrupt method in Ruby.

Exposed the method in Qpid::Proton::Messenger. Also provided the
Qpid::Proton::Error::InterruptedError type that is thrown when
necessary.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1543112 13f79535-47bb-0310-9956-ffa450edef68