4229 mdb hangs on exit when long umem cache names exist
Reviewed by: Robert Mustacchi <rm@joyent.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
	[illumos-gate merge]

commit 065c692a88e4dcdd0c6eadc2476c046d6ee9dd1c
    4229 mdb hangs on exit when long umem cache names exist