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

rescue/rescue/Makefile

@@ -85,6 +85,10 @@ CRUNCH_ALIAS_ln= link
 CRUNCH_ALIAS_rm= unlink
 CRUNCH_ALIAS_ed= red
 
+CRUNCH_PROGS_bin+= pkill
+CRUNCH_SRCDIR_pkill= ${.CURDIR}/../../usr.bin/pkill
+CRUNCH_ALIAS_pkill= pgrep
+
 .if ${MK_RCMDS} != "no"
 CRUNCH_PROGS_bin+= rcp
 .endif
@@ -190,6 +194,8 @@ CRUNCH_BUILDOPTS_dhclient= -DRELEASE_CRUNCH -Dlint
 # 
 CRUNCH_SRCDIRS+= usr.bin
 
+CRUNCH_PROGS_usr.bin= head mt sed tail tee
+
 CRUNCH_PROGS_usr.bin+= gzip
 CRUNCH_ALIAS_gzip= gunzip gzcat zcat
 
@@ -211,7 +217,10 @@ CRUNCH_ALIAS_id= groups whoami
 # 
 CRUNCH_SRCDIRS+= usr.sbin
 
-CRUNCH_PROGS_usr.sbin+= chroot
+CRUNCH_PROGS_usr.sbin= chroot
+
+CRUNCH_PROGS_usr.sbin+= chown
+CRUNCH_ALIAS_chown= chgrp
 
 ##################################################################
 #  The following is pretty nearly a generic crunchgen-handling makefile