many *.m4 files: improve m4 quoting

many *.m4 files: improve m4 quoting

99% of this change was performed by running the following commands:
git ls-files | grep '\.m4$' | xargs perl -pi \
  -e 's/(AC_\w+\()([^[()]+?)([,)])/$1\[$2]$3/g;' \
  -e 's/(AC_\w+\((?:\[[^,]+?\], ){1})([^,[()]+?)([,)])/$1\[$2]$3/g;' \
  -e 's/(AC_\w+\((?:\[[^,]+?\], ){2})([^,[()]+?)([,)])/$1\[$2]$3/g;' \
  -e 's/(AC_\w+\((?:\[[^,]+?\], ){3})([^,[()]+?)([,)])/$1\[$2]$3/g'
perl -pi -e 's/\[\.\.\.\]/.../' m4/onceonly.m4

The remainder were to add Copyright dates, increment serial numbers,
undo some changes in comments, exclude m4/intl.m4, and add quotes
around the "1" in ",1" where the unusual spacing prohibited the
above regexps from doing the job.  For more details, see
<http://thread.gmane.org/gmane.comp.lib.gnulib.bugs/16175>.