Integration tests for ami-describe-anscestors
Installation instructions
Fix race condition in integration test for ami-describe-anscestors

This also exposed a hazard in the interface for ResourceWatcher.waiton, which
is now fixed via the STATES member. (Or more accurately, is partly fixed in
general, and fixable the rest of the way by a ResourceWatcher subclass, which
is where it needs to be fully customized.)