Add "Logger" utility, which maintains vector clocks for each actor.
Merge branch 'master' of github.com:colin-scott/sts2-interposition
Remove extraneous print messages
Merge commit '29e11b8df4c79a92ce1ff062ffe5d8553d19b0a2' into colin-rbcast

Conflicts:
	interposition/src/main/scala/verification/schedulers/Util.scala