tests: use local dir for output

Reported by Kiyoshi KANAZAWA in: http://bugs.gnu.org/18679
* tests/unpack-invalid: Use local directory, not /tmp, for output.
gnulib+bootstrap: update to latest

* gnulib: Update the submodule.
* bootstrap: Update from gnulib.
maint: avoid false positive match in check for double semicolon

* cfg.mk (exclude_file_name_regexp--sc_prohibit_double_semicolon):
Exempt the file, lib/match.c, from gnulib's new double-semicolon
check.
maint: enable more syntax checks

* cfg.mk (local-checks-to-skip): Remove several rule names from this
list, thus enabling the corresponding checks.  To fix some, I made
syntactic changes to source files.  In other cases, I exempted certain
files from the checks.
Add exemptions for these:
  sc_prohibit_atoi_atof = ^(gzip|sample/sub)\.c$$
  sc_space_tab = ^lib/match\.c$$
  sc_useless_cpp_parens = ^(lib/match\.c|tailor\.h)$$
* configure.ac: Add quotes to fix under-quoting.
* deflate.c: Remove unnecessary cpp parentheses.
* tests/Makefile.am (TEST_ENVIRONMENT): Remove space-before-TAB.
* unlzw.c: Change some TABs to spaces.
gzip: adjust -v output when -k is also specified

Problem reported by Eric Benoit in: http://bugs.gnu.org/16401
* gzip.c (treat_file): When keeping a file, don't say it's replaced.
* NEWS: Document this.
* tests/keep: Test this.
maint: move new NEWS entry into block for upcoming release

* NEWS: Move the latest NEWS entry from the block for gzip-1.6
into the block for the upcoming release.