Deactivate the installation of config files not relevant to OS X.

It would be nicer if this were conditional on the target but,
since this project is specific to OS X, this should be fine.
Add an entry to $syscondfir/paths.d/ if $prefix is not the default path.
Install the launchd item that will run 'zpool import' on system startup.

Installs only if $sysconfdir is set to /etc. Too prudent perhaps?