Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Fix style nit: don't use leading zero for dates in .Dd

Prompted by: brueffer
Approved by: brueffer
MFC after: 3 days

Update manpage to remove CRT reference.

PR: 154441
Submitted by: Ben Haga (bhaga of absoludicrous com)
Suggestion by: pluknet
Approved by: keramida (mentor)
MFC after: 3 days

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)