Cleanup scheduler-process protocol
Support for exit/2, send_after/3, start_timer/3
Fix a race condition

Messages might be seen by the unblocking mechanism, but not be
instrumented properly. Flipping the order of instrumentation and
checking for unblocking obviously fixes that.
Instrument port_command/2, port_command/3, port_control/3
Use --ignore-timeout flag for start_timer and send_after
Merge branch 'exits-timers-afters'

Conflicts:
	src/concuerror_rep.erl
	src/concuerror_sched.erl
Wait for uninstrumented messages to be processed