strtod, strtold: Use the locale's decimal point.

strtod, strtold: Use the locale's decimal point.

* lib/strtod.c: Include <locale.h>, <stdio.h>, <langinfo.h>.
(decimal_point_char): New function, copied from lib/vasnprintf.c.
(parse_number): Add a radixchar argument. Use it instead of '.'.
(STRTOD): Invoke decimal_point_char and pass the result to parse_number.
* m4/strtod.m4 (gl_PREREQ_STRTOD): Test whether nl_langinfo exists.
* m4/strtold.m4 (gl_PREREQ_STRTOLD): Likewise.
* tests/test-strtod1.c: New file.
* tests/test-strtod1.sh: New file.
* modules/strtod-tests (Files): Add test-strtod1.{sh,c}. Add
locale-fr.m4 and its dependencies.
(configure.ac): Invoke gt_LOCALE_FR, gt_LOCALE_FR_UTF8.
(Makefile.am): Arrange to compile test-strtod1.c and run
test-strtod1.sh.
* tests/test-strtold1.c: New file.
* tests/test-strtold1.sh: New file.
* modules/strtold-tests (Files): Add test-strtold1.{sh,c}. Add
locale-fr.m4 and its dependencies.
(configure.ac): Invoke gt_LOCALE_FR, gt_LOCALE_FR_UTF8.
(Makefile.am): Arrange to compile test-strtold1.c and run
test-strtold1.sh.