Allow GEOM_VINUM to be statically compiled into the kernel.

Submitted by:	gleb
MFC after:	3 days
Add -J command/flag to filter by jail name/jid. This will automatically
display the JID as well (the -j command/flag).

  0 displays host.
  + displays all.

MFC after:	2 weeks
Relnotes:	yes
- Add a hint for 'u' and 'J' command that '+' displays all.

MFC after:	2 weeks