RFC: top displays jail id

[Rong-en Fan]

Hi all,

The patch at

http://people.freebsd.org/~rafan/top.diff

makes top display jail id by -j or 'j' key. This is originally created
by clsung@ (thank you). For example,

  PID JID USERNAME     THR PRI NICE   SIZE    RES STATE  C   TIME   WCPU COMMAN
89573   0 mysql         14   4    0   169M   145M sbwait 0  82:37  0.00% mysqld
83920   4    106         2  96    0 81220K 72176K ucond  1  20:52  0.00% clamd
62776   3 mysql          5  20    0 65428K 32364K kserel 0   7:27  0.00% mysqld
55862   0 rafan          1  96    0 28644K 23952K select 0   4:39  0.00% screen
10245   0 rafan          1  96    0 32816K 10736K select 0   3:46  0.00% irssi
89643   0 wckao          1  96    0 21596K  6176K select 0   2:45  0.00% irssi
34259   4 mysql          9  20    0 55716K 30180K kserel 0   2:26  0.00% mysqld
25616   4 root           1  96    0 14404K  2580K select 0   2:11  0.00% master

Now I know which mysqld is in jail. If no objections, I will commit to
HEAD later
today and merge to 6.x in 2 weeks.

Regards,
Rong-En Fan