Make Channel and Connection implement AutoCloseable for use in try-with-...

...resources

As mentioned in the description, this change will allow Connection and Channel instances to be compatible with the try-with-resources feature: http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

For try-with-resources to work, both interfaces need to extend AutoCloseable.  Since each interface already declares a close() method with the proper signature, the change is trivial.