Initial ZFS support. Just the runtime support, no support for actually

creating the initial ZFS volumes, that is described in Mike's notes
file on how to setup ZFS on ops. But once that is done, the runtime
supports takes care of creating volumes for users and projects/groups.
New configure variables, with defaults to:

	WITHZFS=0
	ZFS_ROOT=z
	ZFS_QUOTA_USER="1G"
	ZFS_QUOTA_PROJECT="100G"
	ZFS_QUOTA_GROUP="10G"