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

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

Drop build option switch for the older GNU patch.

As promised, drop the option to make the older GNU patch
the default.

GNU patch is still being built but something drastic may
happen to it to it before Release.

Make the BSD-licensed patch the default.

The BSD-licensed patch(1) command has matured and it's behaviour
can be considered equivalent to the older version of GNU patch
in the tree.

The switch has been extensively tested [1] and only two ports
presented regressions, which have since been fixed.

For convenience a new WITH_GNU_PATCH option is available,
but it will likely be removed in the near future.

PR: 176313
Approved by: portmgr

- Refresh code with latest OpenBSD revisions.
- Remove $DragonFly$ tags as they are using git nowadays and VCS tags will
not help merging.
- Other changes to Copyright headers to make them consistent with other
source code, we intend to fork from this point.

Reviewed by: pfg

- Add a BSD-licensed patch, ported by Pedro F. Giffuni (pfg) from
DragonflyBSD and install it as bsdpatch. WITH_BSD_PATCH makes it
default and installs GNU patch as gnupatch.

Submitted by: pfg
Obtained from: The DragonflyBSD Project