Replace the GNU gzip with a slightly modified NetBSD gzip. The

NetBSD version is a feature-to-feature re-implementation of GNU
gzip using the freely-redistributable zlib and this version is
expected to be mostly bug-to-bug compatible with the GNU
implementation.

 - Because this is a piece of mature code and we want to make
   changes so it is added directly rather than importing to
   src/contrib.
 - Connect newly added code to src/usr.bin/ and rescue/rescue
   build.
 - Disconnect the GNU gzip code from build for now, they will
   be eventually removed completely.
 - Provide two new src.conf(5) knobs, WITHOUT_BZIP2_SUPPORT and
   WITHOUT_BZIP2.

Tested by:	kris (full exp-7 pointyhat build)
Approved by:	core (importing a 4-clause BSD licensed file)
Approved by:	re (adding new utility during -HEAD code slush)

gnu/usr.bin/Makefile

@@ -15,7 +15,6 @@ SUBDIR= bc \
 	${_gperf} \
 	grep \
 	${_groff} \
-	gzip \
 	${_man} \
 	patch \
 	${_rcs} \