kqueue: (wip) Fix for data races.

Added missing lock in `Watch` method.
kqueue: (wip) Fix for incorrectly detected event.

kqueue may return more events than requested
if one of them is filtered.
Merge pull request #37 from pblaszczyk/kqueue

kqueue: Fix issue with data races & incorrectly forwarded events.
Reconfigure Travis CI to build under Mac OS X