Commit Briefs
disk/mkfs,disk/mkext: fix mkdir conflict
R=rsc http://codereview.appspot.com/6445076
disk/mkfs, disk/mkext: add from Plan 9
R=rsc, rsc http://codereview.appspot.com/6405057
R=rsc http://codereview.appspot.com/6445076
R=rsc, rsc http://codereview.appspot.com/6405057