(<langinfo.h>): Include if HAVE_LANGINFO_H.

(<langinfo.h>): Include if HAVE_LANGINFO_H.
(DATE_FMT_LANGINFO): New macro, taken from sh-utils/src/date.c.
(print_long_format): Use it to determine "date" format.
Do not wrap "%b %e %Y" and "%b %e %H:%M" in _(), as it results in
incorrect behavior when LC_ALL is unset, LC_TIME is "C", and
LC_MESSAGES or LANG is set to something disagreeing with the POSIX
locale.