[fsnotify] report #6

[Ilya Putsikau]

Done this week:
* Add regression tests
* Fix vnode neg ref cnt in namei() panic
* Use same struct field names as in Linux
* Return as many events as possible in single read()
* Return ENIVAL if buffer is too small for next event
* Close fd before adding watch (if FN_CLOSEFD given)
* Remove inactive events
* Don't update node path during destroy events or if use count is zero