INT-2900 Remove Extraneous Debug Log

When referencing a <gateway/> from a <service-activator/>, a debug
log is written with a full stack trace.

This is because all methods on the proxy are considered candidates,
but one method (addAdvice) has multiple parameters and can't be
used to process a message.

Add code to detect a proxy that has no target object; if the Proxy
only has one interface, then use that as the targetClass.
Merge pull request #733 from garyrussell/INT-2900

* INT-2900: Remove Extraneous Debug Log