MFC r263459 (MFV 263436-263438):

  3947 zpool(1M) references nonexistent zfs-features(5)
  4540 zpool(1M) man page doesn't describe "readonly" property
  3948 zfs sync=default is not accepted
  4611 zfs(1M) still mentions 'send -r' in synopsis
  4415 zpool(1M) man page missing "import -m" description
  4570 Document dedupditto pool property
  4572 Dedup-related documentation additions for zpool and zdb.
  1371 Add -D option description to zpool(1M) manpage
  4571 Add documentation for -T and interval to "zpool list"
MFC r263889: MFV r263887:

3993 zpool(1M) and zfs(1M) should support -p for "list" and "get"
4700 "zpool get" doesn't support -H or -o options
MFC: nc(1) from OpenBSD 5.5.