This works with existing inotify/EVFILT_VNODE functionality to
propagate changes made from one Maildir to another Maildir.
I chose the lei/store worker process to handle this since
propagating changes back into lei-daemon on a massive scale
could lead to dead-locking while both processes are attempting
to write to each other. Eliminating IPC overhead is a nice
side effect, but could hurt performance if Maildirs are slow.
The code for "lei export-kw" is significantly revamped to match
the new code used in the "lei/store" daemon. It should be more
correct w.r.t. corner-cases and stale entries, but perhaps
better tests need to be written.
squashed:
t/lei-auto-watch: increase delay for FreeBSD kevent
My FreeBSD VM seems to need longer for this test than inotify
under Linux, likely because the kevent support code needs to be
more complicated.