Fix comments.

Sponsored by:	EMC / Isilon Storage Division
Migrate tools/regression/usr.bin/pkill to the new tests layout.

Interestingly, the pkill tool lives in bin, not usr.bin.  Haven't bothered
to check if this is because the tool moved or because the tests were
originally added in the wrong place.
Make the priv test program exit with non-zero if any failures are detected.

And, mind you, this already returns a failure :-/
errx prepends the program name to the message; don't do it by hand.
Make the error message more clear.

Sponsored by:	The FreeBSD Foundation
Include strings.h so that bpf_filter.c can be built in userland.

This is to bring in a definition for bzero(3), which in turn allows the
tests in tools/regression/bpf/ to build again.