MFC r351836, r351866, r354328: patch(1) /dev/null testing+improvement

r351836: patch(1): add some basic tests

Summary:
- basic: test application of patches created by diff -u at the
beginning/middle/end of file, which have differing amounts of context
before and after chunks being added
- limited_ctx: stems from PR 74127 in which a rogue line was getting added
when the patch should have been rejected. Similar behavior was
reproducible with larger contexts near the beginning/end of a file. See
r326084 for details
- file_creation: patch sourced from /dev/null should create the file
- file_nodupe: said patch sourced from /dev/null shouldn't dupe the contents
when re-applied (personal vendetta, WIP, see comment)
- file_removal: this follows from nodupe; the reverse of a patch sourced
from /dev/null is most naturally deleting the file, as is expected based
on GNU patch behavior (WIP)

r351866: patch(1): fix the file removal test, strengthen it a bit

To remain compatible with GNU patch, we should ensure that once we're
removing empty files after a reversed /dev/null patch we don't remove files
that have been modified. GNU patch leaves these intact and just reverses the
hunk that created the file, effectively implying --remove-empty-files for
reversed /dev/null patches.

r354328: patch(1): give /dev/null patches special treatment

We have a bad habit of duplicating contents of files that are sourced from
/dev/null and applied more than once... take the more sane (in most ways)
GNU route and complain if the file exists and offer reversal options.

This still falls short a little bit as selecting "don't reverse, apply
anyway" will still give you duplicated file contents. There's probably other
issues as well, but awareness is the first step to happiness.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Remove automatic checkout feature.

Obtained from: DragonFly via OpenBSD
Relnotes: yes
MFC: never

patch(1): small include changes.

Mostly to match OpenBSD, no functional change.

Obtained from: OpenBSD

Fixes to exit status.

Exit with EXIT_FAILURE for invalid arguments.
Fixes NetBSD-PR 43517.

Print version string to stdout instead of stderr;
it is user-requested and not an error.

Obtained from: NetBSD
MFC after: 5 days

patch: Bring in xstrdup and use it when appropriate.

The function savestr allows NULL return values during Plan A patching so in
case of out of memory conditions, Plan B can step in. In many cases, NULL
value is not properly handled, so use xstrdup here (it's outside Plan A/B
patching, which means that even Plan B relies on successful operations).

Clean up some whitespaces while here

Obtained from: OpenBSD
MFC after: 2 weeks

Improve bsdpatch usability:

- Ask only once for "Apply anyway". [1]
- Tell user what file have failed patch rather than just how
many hunks failed.

Reported by: jmg via pfg [1]
Tested by: pfg [1]
Approved by: re (gjb)

Fix file selection logic for the RCS/SCCS case, as was done for the simple
file case before. Bump version because of the changed behavior, which now
matches the documentation.

Reviewed by: pfg

Revert r250972 to fix build.

The error handling for writes to the target file could lead to the final
fclose() being skipped. Fix this by using boolean "&" and "|" instead of
short-cut operators "&&" and "||".
While here, increment the last part of the version string. The reason is
the fixed output file selection logic in pch.c, which was committed as
r250943, yesterday.

Reviewed by: pfg

patch: Follow original versioning convention.

According to the README file [1] the 12u variant, unlike
the 12g variant, contains no copyleft code. It is therefore
convenient to keep using the original versioning scheme to
prevent confusions.

[1] http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/patch/README

- 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