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.

scripts/dump-remind.in

@@ -9,7 +9,7 @@
 # be put in the tape drive.
 #
 
-# Include location of `sendmail' and GNU finger.
+# Include location of 'sendmail' and GNU finger.
 PATH="/usr/lib:/usr/local/gnubin:${PATH}"
 export PATH
 
@@ -25,8 +25,8 @@ MT_OFFLINE
 # which users are logged into consoles (and thus in the office and capable
 # of changing tapes).
 #
-# Certain users (like `root') aren't real users, and shouldn't be notified.
-# Neither should `zippy', `elvis', etc. (on the GNU machines) since they're
+# Certain users (like 'root') aren't real users, and shouldn't be notified.
+# Neither should 'zippy', 'elvis', etc. (on the GNU machines) since they're
 # just test accounts.
 recipients="`
     finger .clients 2> /dev/null \