5292 findunref is both slow and broken
Reviewed by: Igor Kozhukhov <ikozhukhov@gmail.com>
Reviewed by: Joshua Clulow <josh@sysmgr.org>
Reviewed by: Gordon Ross <gwr@nexenta.com>
Approved by: Dan McDonald <danmcd@omniti.com>
	[illumos-gate merge]

commit b998737654179ec0e068e04f6fda6e76777171c9
    5292 findunref is both slow and broken