Jan Kiszka reported high polling frequency when using -watch.
It turns out OS-specific packages for Filesys::Notify::Simple do
not pull in interfaces to use kqueue or inotify, which are
required to perform power-efficient event-based wakeups on
Maildir writes.
Fix the name of the Filesys::Notify::Simple for FreeBSD while
we're at it.
Link: https://public-inbox.org/meta/c85803c6-6d77-a300-491a-9f310dd284c1@web.de/