inotify: do not rely on stat(.hg/dirstate) to invalidate our dirstate
stat() is not reliable when several events happen quickly. Which means
that if two hg actions occur in the same second, stat() result will not
reflect the second change. And only _one_ invalidate() call was done.
Also ignore the events that occur when wlock is held, since wlock release
will trigger a full rescan anyway.
Fixes 17 run-tests.py --inotify tests.