NULL does not need a cast

Fix memory leaks.

Include nbtool_config.h for tool builds.

Replace usr.bin/grep with the BSD grep implementation from FreeBSD.

Import of our changes to grep developed in othersrc. A very
brief summary:

* Add NetBSD RCS Ids. Change to use a date based version number.
* Remove unused variables and functions.
* Move towards Ne

Import of our changes to grep developed in othersrc. A very
brief summary:

* Add NetBSD RCS Ids. Change to use a date based version number.
* Remove unused variables and functions.
* Move towards NetBSD code style.
* Add missing GNU options (except for --include, --exclude and
--line-buffered)
* Bug fixes
* Bug fixes and changes from OpenBSD's src/usr.bin/grep

A full list of changes can be viewed in the NetBSD CVS repository at
othersrc/usr.bin/grep. A ChangeLog is also available at:
ftp://ftp.NetBSD.org/pub/NetBSD/misc/cjep/grep-ChangeLog.txt

If you want to help out, please let me (cjep@) know so that we can
organise our efforts efficiently.

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Import of BSD-licensed grep by James Howard and Dag-Erling Coïdan
Smørgrav. This import is of version 0.16.