[Nut-upsuser] New Mac OS X UPS monitoring driver

[Charles Lepple]

Mac users,

I just committed (in r3704) a new driver which monitors the built-in
UPS driver in Mac OS X. Basically, if your USB-based UPS shows up in
the Energy Saver system preferences panel, this driver should be able
to monitor that UPS.

There is limited functionality in this first release, but I'm looking
for feedback on how well it compiles on various systems, and whether
it works with hardware other than what I had lying around. Please post
success or failure reports to this list (or nut-upsdev).

Basic setup instructions are in the man page:
http://buildbot.networkupstools.org/~buildbot/cayenne/docs/r3704-211/man/macosx-ups.html

A ZIP snapshot of the SVN tree is available on the GitHub mirror:
https://github.com/clepple/nut (SVN trunk is the master branch there)

The use case I imagined was to leverage the NUT protocol to monitor
state-of-charge while the UPS recovers from a deep discharge. There is
currently no Low Battery signal from the OS prior to a shutdown,
although it could be synthesized after one of the shutdown warnings. I
would like to add that to a future release. I am also curious if
people have tried third party drivers such as PowerChute (which might
not populate this data store).

Note that this is orthogonal to the problem of other NUT USB drivers
being unable to attach to an UPS when the OS has already claimed it.
That problem has already been solved, but I just need to find some
time to integrate that with our autoconf setup.

- Charles