Server/Core: also shutdown on exceptions during fam blocking

Previously the server got stuck, if a keyboard interrupt occured during
block_for_fam_events. The KeyboardInterrupt exception was only handled
in the executable and it does not call shutdown for the Core. So the
running fam thread does not get killed and the main thread waits for it.
Merge pull request #222 from AlexanderS/fix-keyboard-interrupt

Server/Core: also shutdown on exceptions during fam blocking