inotify queues IN_MOVED_FROM and IN_MOVED_TO of a rename one after the
other. The watcher thread could read the first before the second was
queued and report a rename inside the directory as a move to another
directory (NOTE_WRITE | NOTE_EXTEND instead of NOTE_WRITE), which made
guest_kqueue abort on loaded runners.
The watcher now reads the queue until it is empty and, when a move half
has no partner, calls getdents64 on the directory before reading again:
that takes the directory lock rename holds until both halves are queued.
59fcdea9c4