Consider backporting Inotify add_watch() initialization fix to Pike 8.0

Imported from https://youtrack.roxen.com/issue/PIKE-67

Reported by Marcus Wellhardh wellhard@roxen.com

commit 046e0844
Author: Henrik Grubbström (Grubba) grubba@grubba.org
Date: Wed Jun 14 11:59:04 2017 +0200

Inotify: Improved initialization in add_watch().

Make sure that the backend is woken up after scheduling the
artifical initialization events. Otherwise they may stay
pending indefinitely.