Added support for custom listener interfaces.

git-svn-id: https://svn.apache.org/repos/asf/camel/trunk@1460463 13f79535-47bb-0310-9956-ffa450edef68
Improved Guava EventBus component Javadoc.

git-svn-id: https://svn.apache.org/repos/asf/camel/trunk@1460465 13f79535-47bb-0310-9956-ffa450edef68