Print gathered results after interrupted run

[mvz]

trafficstars

mutest's run time may be very long if there are many mutations to consider. If the user interrupts this, it would be useful to print the set of live mutations already discovered (similar to how RSpec prints failed specs).

[dgollahon]

@mvz: Yeah, I agree. I've been wanting that myself for a while. There's definitely work to be done on the reporter.