POSIX.1 states that `dbm_nextkey` must return an invalid key
(i.e., `key.dptr == NULL`) after the end of the database was reached.
The current implementation of `hash_seq` will incorrectly restart
the key sequence after the end of the database is reached.

Fix this by checking the "current bucket" index when R_NEXT is passed.

Sponsored by:   Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D51635
Reviewed by:	markj

The dbm(3) manpage explicitly states that O_WRONLY is not allowed in
dbm_open, but a more recent comment in ` __hash_open` suggests otherwise.
Furthermore, POSIX.1 allows O_WRONLY in dbm_open and states
that the underlying file must be opened for both reading and writing.

Fix this by correcting the O_WRONLY check and moving it further into
the function to make sure that the original flags are stored in hashp.

Sponsored by:   Klara, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D51514

Sponsored by:   Klara, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D51492

This is a residual of the $FreeBSD$ removal.

MFC After: 3 days (though I'll just run the command on the branches)
Sponsored by: Netflix

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

Sponsored by:	Dell EMC Isilon

This contains some new testcases in /usr/tests/...:

- .../lib/libc
- .../lib/libthr
- .../lib/msun
- .../sys/kern

Tested on:	amd64, i386
MFC after:	1 month

r305358

MFC after:	59 days
X-MFC with:	r305358
Reported by:	Jenkins, rodrigc
Sponsored by:	EMC / Isilon Storage Division

- Some of the lib/libc and lib/thr tests fail
- lib/msun/exp_test:exp2_values now passes with clang 3.8.0

The Makefiles in contrib/netbsd-tests were pruned as they have no value

Sponsored by: EMC / Isilon Storage Division

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