- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

Incorporate recent changes from NetBSD. Most notable change is the addition
of support of decompressing xz files.

Obtained from: NetBSD

Match symbolic link handling behavior with GNU gzip, bzip2 and xz:

When we are operating on a symbolic link pointing to an existing
file, bail out by default, but go ahead if -f is specified.

Submitted by: arundel
MFC after: 2 weeks

Language improvements to make the BUGS section easier to read.

Reviewed by: Alexander Best <alexbestms wwu de>
MFC after: 13 days

Diff reduction against NetBSD and add myself to AUTHORS section of the
manual page as I wrote the unpack functionality. No actual executable
code change verified with md5(1).

Sync with NetBSD:
- gzip -n does not store timestamp; [1]
- Reduce diff against NetBSD by moving some casts in our local
versions.

PR: bin/134955
Obtained from: NetBSD
MFC after: 1 month

Sync with NetBSD's license changes.

Make it clear that gzcat expects each argument to be separate files.

PR: docs/123010
Submitted by: Andrew Wright <andrewhw ieee org>
MFC after: 2 weeks

Mention 'k' option of gunzip.

Pointed out by: ighighi gmail.com

Add a '-k' flag which is similar with its bzip2(1) counterpart,
meaning that the user wants the input file to be left intact.

Feature request: Ighighi <ighighi gmail.com>
PR: bin/103006
MFC after: 1 month

Mention a limitation that was inherted from RFC1952, making
it impossible to obtain correct file size from a file that
is larger than 4GB before compression.

PR: bin/110329
MFC after: 1 week

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)