Followed my plan from yesterday, and wrote a simple C library to interface
to `kqueue`, and Haskell code to use that library. By now I think I
understand kqueue fairly well -- there are some very tricky parts to the
interface.

But... it still didn't work. After building all this, my code was
failing the same way that the
[haskell kqueue library failed](https://github.com/hesselink/kqueue/issues/1)
yesterday. I filed a [bug report with a testcase]().

Then I thought to ask on #haskell. Got sorted out in quick order! The
problem turns out to be that haskell's runtime has a periodic SIGALARM,
that is interrupting my kevent call. It can be worked around with `+RTS -V0`,
but I put in a fix to retry to kevent when it's interrupted.

And now `git-annex watch` can detect changes to directories on BSD and OSX!

Note: I said "detect", not "do something useful in response to". Getting
from the limited kqueue events to actually staging changes in the git repo
is going to be another day's work. Still, brave FreeBSD or OSX users
might want to check out the `watch` branch from git and see if 
`git annex watch` will at least *say* it sees changes you make to your
repository.