Merge recent zfs vendor changes, sync code and adjust userland DEBUG.
Illumos issued covered:
1884 Empty "used" field for zfs *space commands
3006 VERIFY[S,U,P] and ASSERT[S,U,P] frequently check if first argument
is zero
3028 zfs {group,user}space -n prints (null) instead of numeric GID/UID
3048 zfs {user,group}space [-s|-S] is broken
3049 zfs {user,group}space -t doesn't really filter the results
3060 zfs {user,group}space -H output isn't tab-delimited
3061 zfs {user,group}space -o doesn't use specified fields order
3064 usr/src/cmd/zpool/zpool_main.c misspells "successful"
3093 zfs {user,group}space's -i is noop
3098 zfs userspace/groupspace fail without saying why when run as non-root
References:
https://www.illumos.org/issues/ + [issue_id]
Obtained from: illumos (vendor/illumos, vendor/illumos-sys)
MFC after: 2 weeks
4c5238d576