Fix broken import in ProtocolTest

I think this only broke when ALL my other patches were merged such that
sbtrc was completely gone, even though the other patches all compiled
separately. Or something.
CanCancelTasks test: always wait for both executions when recording events

This way we don't miss one of the executions completing.
Log some details of the execution cancel process

This lets us see what's gone wrong, if something has.
Don't special-case canceling items which are still in queue

Just mark them canceled and let them get to the front of the
queue where they should immediately fail.

Fixes #213
Merge pull request #215 from sbt/wip/havocp-one-cancel-codepath

Try harder to fix CanCancelTasks integration test