Early exit if nothing to do on merge event

Change-Id: I9cc6ec8e233cfac98d482be76d8e7ed6567c46ff
Add copious amounts of logging

It's easy to turn down the logging, it's hard to find out about
things you haven't logged. Also update libfritter for logging
improvements there.

Change-Id: I59100b49a1f94fc06b0767225f93afd3a7ae5713