Add some essential tools to rescue(8) in order to make it a versatile emergency tool:
Add some essential tools to rescue(8) in order to make it
a versatile emergency tool:

o sed(1) as a multi-purpose text filter -- can do grep's job and much more.
o head(1), tail(1), and tee(1) as idiomatic text filters.
o mt(1) to control tape drives (PR misc/98383).
o chown(8) aka chgrp(8) to complement the ch* subset.
o pkill(1) aka pgrep(1) to control running processes easily and thus to be
  able to recover from a serious problem or a fatal typo in an otherwise live
  system w/o a reboot.  (It also deserves adding to rescue(8) for its having
  triggered a latent bug in crunchgen(1), but we had better add a regression
  test for that. :-)

The resulting change in rescue(8) size has the following order of magnitude
on i386: 3787656 - 3727872 = 59784, i.e. just a tad.

Discussed on:   -hackers (I seem to have wearied all opponents :-)
PR:             misc/98383

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase