10592 misc. metaslab and vdev related ZoL bug fixes
Portions contributed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: Giuseppe Di Natale <guss80@gmail.com>
Reviewed by: George Melikov <mail@gmelikov.ru>
Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: Tony Hutter <hutter2@llnl.gov>
Reviewed by: Kody Kantor <kody.kantor@joyent.com>
Approved by: Dan McDonald <danmcd@joyent.com>

*** 109,121 ****
               If the -q option is also specified, don't print the labels.
  
               If the -u option is also specified, also display the uberblocks
               on this device.
  
!      -L      Disable leak tracing and the loading of space maps.  By default,
!              zdb verifies that all non-free blocks are referenced, which can
!              be very expensive.
  
       -m      Display the offset, spacemap, and free space of each metaslab.
  
       -mm     Also display information about the on-disk free space histogram
               associated with each metaslab.
--- 109,121 ----
               If the -q option is also specified, don't print the labels.
  
               If the -u option is also specified, also display the uberblocks
               on this device.
  
!      -L      Disable leak detection and the loading of space maps.  By
!              default, zdb verifies that all non-free blocks are referenced,
!              which can be very expensive.
  
       -m      Display the offset, spacemap, and free space of each metaslab.
  
       -mm     Also display information about the on-disk free space histogram
               associated with each metaslab.