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

Set st_nlink in the stat structure within the inode to 1 as well.
The cd9660 file system uses that field for the link count and it
was 0. This impacts pwd_mkdb(8) as it checks for st_nlink not being
0 as part of closing a race.

Support hardlinks in manifest files by the same logic as the treewalk
code.

Reviewed by: marcel
Sponsored by: DARPA, AFRL

Allow '.' components in manifest paths. They are always the first
component of mtree -C and install -M output and are easily skipped.

Reviewed by: marcel
Sponsored by: DARPA, AFRL

Fix the -N option in manifest mode by using pwcache(3). This also
speeds up image creation appreciably.

Reviewed by: marcel
Sponsored by: DARPA, AFRL

Add a -D flag that causes duplicate entries in an mtree manifest to be
treated as warnings rather than errors.

Reviewed by: marcel
Sponsored by: DARPA, AFRL

If no contents keyword is specified, the default for files is
the named file.

Approved by: marcel (mentor)

Add support for using mtree(5) manifest files to define the image
to be created. The support is based on mtree version 2.0, as used
in libarchive, but adds new features on top of it.

The current implementation is fully functional, but is envisioned
to grow at least the following additional features over time:
o Add support for the /include special command so that manifest
files can be constructed using includable fragments.
o Add support specifying a search path to locate content files.
o Content file filters: commands that provide file contents on
stdout.

The manifest file eliminates the need to first construct a tree
as root in order to create an image and allows images (releases)
to be created directly from object trees and/or source trees.

Reviewed by: deo
Sponsored by: Juniper Networks, Inc