tar: quote 'like this', not `like this'

This fixes some test failures recently introduced by gnulib updates
prompted by recent changes to the GNU coding standards,
which now advise to use quotes 'like this' or "like this"
rather than `like this'.
* NEWS: Document this.
* README, README-hacking, doc/Makefile.am, scripts/backup.in:
* scripts/backup.sh.in, scripts/dump-remind.in:
* src/buffer.c, src/checkpoint.c, src/create.c, src/incremen.c:
* src/misc.c, src/names.c, src/sparse.c, src/transform.c:
* tests/incr02.at, tests/incremental.at, tests/multiv08.at:
* tests/sparse04.at, tests/star/README, tests/update01.at:
Quote 'like this' in comments.
* src/tar.h:
Quote "like this" in comments, when quoting English phrases rather
than code.
* configure.ac:
* scripts/xsparse.c (get_var, read_xheader, main):
* src/compare.c (diff_archive):
* src/extract.c (prepare_to_extract):
* src/tar.c (request_stdin, tar_set_quoting_style, doc, options)
(set_subcommand_option, report_textual_dates, parse_opt)
(decode_options, main):
* src/xheader.c (decx):
Quote 'like this' in diagnostics.
* doc/tar.texi (list, warnings, override)
(Selecting Archive Members, quoting styles, after, hard links)
(Sparse Recovery, Multi-Volume Archives, label):
Adjust documentation to match new output.
* tests/backup01.at, tests/incr01.at, tests/incr04.at:
* tests/label04.at, tests/label05.at, tests/link03.at:
* tests/listed02.at, tests/multiv03.at, tests/multiv05.at:
* tests/rename01.at, tests/rename02.at, tests/rename03.at:
* tests/volume.at:
Adjust tests to match new quoting behavior.

tests/label05.at

@@ -40,7 +40,7 @@ tar -rf archive file
 ],
 [# Create volume
 # Update: wrong label
-tar: Archive not labeled to match `My volume'
+tar: Archive not labeled to match 'My volume'
 tar: Error is not recoverable: exiting now
 # Update: right label
 ],[],[],[gnu,oldgnu,posix])