kqueue: Fix for panic in tests.
kqueue: Fix for panic in tests.

If files to be processed no longer exist, monitor will not panic during
walking through them. If they were already monitored, kqueue will send
removal events. If they weren't, events are lost. Might later consider
option to generate triggers based on context if determining them is
possible. #63

Zillode/notify,pblaszczyk/notify,Fiery/notify,rjeczalik/notify