Change instrumenter to enqueue all messages

This change requires that the scheduler kick off processing of messages
after quiescence (including right after being started) but has the nice property
that things are recorded consistently and everything is simple.
Change schedulers to switch to new instrumenter

The scheduler semantics are unaffected with this change
Fix peek scheduler to not double count messages
Merge pull request #10 from apanda/master

Fix the problem with the missing first event