fsnotify_bsd: fix for some data races

All data races detected in tests, that happens in fsnotify_bsd file are
now fixed. I still need to fix data races in tests.

Related to #29.
tests: fix data races

go test -race does not report any data races in darwin anymore. I still
need to check Linux.

Related to #29.
Merge branch 'issue-29' of https://github.com/fsouza/fsnotify into race
Fixed unlock for watching directory