Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Rename tests from <foo> to <foo>_test to match the FreeBSD test suite
naming scheme

usr.bin/diff/diff_test was renamed to usr.bin/diff/netbsd_diff_test
to avoid collisions with the renamed FreeBSD test.

MFC after: 1 week
Sponsored by: Dell EMC Isilon

Merge ^/user/ngie/release-pkg-fix-tests to unbreak how test files are installed
after r298107

Summary of changes:

- Replace all instances of FILES/TESTS with ${PACKAGE}FILES. This ensures that
namespacing is kept with FILES appropriately, and that this shouldn't need
to be repeated if the namespace changes -- only the definition of PACKAGE
needs to be changed
- Allow PACKAGE to be overridden by callers instead of forcing it to always be
`tests`. In the event we get to the point where things can be split up
enough in the base system, it would make more sense to group the tests
with the blocks they're a part of, e.g. byacc with byacc-tests, etc
- Remove PACKAGE definitions where possible, i.e. where FILES wasn't used
previously.
- Remove unnecessary TESTSPACKAGE definitions; this has been elided into
bsd.tests.mk
- Remove unnecessary BINDIRs used previously with ${PACKAGE}FILES;
${PACKAGE}FILESDIR is now automatically defined in bsd.test.mk.
- Fix installation of files under data/ subdirectories in lib/libc/tests/hash
and lib/libc/tests/net/getaddrinfo
- Remove unnecessary .include <bsd.own.mk>s (some opportunistic cleanup)

Document the proposed changes in share/examples/tests/tests/... via examples
so it's clear that ${PACKAGES}FILES is the suggested way forward in terms of
replacing FILES. share/mk/bsd.README didn't seem like the appropriate method
of communicating that info.

MFC after: never probably
X-MFC with: r298107
PR: 209114
Relnotes: yes
Tested with: buildworld, installworld, checkworld; buildworld, packageworld
Sponsored by: EMC / Isilon Storage Division

import sdiff(1) from GSoC 2012

Import sdiff(1) from the diff version written by Raymond Lai,
improved during GSoC 2012 by Jesse Hagewood.

Compared to the version done in during that summer of code:
- Remove the zlib frontend: zsdiff
- Compatible output (column size and separators) with GNU sdiff

Compared to GNU sdiff in ports:
- The only difference is padding using spaces vs tabs

Compared to OpenBSD and NetBSD import:
- Implement missing options (including long options) from GNU sdiff
- Improved support for the edition mode (signal handling)
- Output visually compatible with GNU sdiff: size of columns

While here import regression tests from NetBSD adapted to fit the output as
expected by GNU sdiff

Reviewed by: emaste (in part)
Obtained from: OpenBSD, NetBSD, GSoC 2012
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D5981
Differential Revision: https://reviews.freebsd.org/D6032 (diff with NetBSD version)
Differential Revision: https://reviews.freebsd.org/D6033 (diff with OpenBSD version)