Zfsd should deactivate a spare if the original device is replaced while the
system is powered off.

cddl/sbin/zfsd/case_file.cc
cddl/sbin/zfsd/vdev.cc
cddl/sbin/zfsd/vdev.h
cddl/sbin/zfsd/vdev_iterator.h
cddl/sbin/zfsd/zfsd.cc
cddl/sbin/zfsd/zfsd_event.cc

        cddl/sbin/zfsd/zfsd_event.h
		When zfsd receives a misc.fs.zfs.resilver_finish event, it
		will iterate through all spare leaf vdevs on the pool.  It
		will detach any that appear to be unnecessary.

Submitted by: alans
Approved by: ken (mentor)
Sponsored by: Spectra Logic Corporation