build: Add gettext support.
Add po/LINGUAS with support for de, es and fr.
Add gettext.h from gettext-0.18.2.1.
gettext.h: Define keywords "_" and "N_."
Am: Initialize locale data.
OBOX.cpp: Mark strings for translation.
OFIRM.cpp: Mark strings for translation.
OFIRMIF.cpp: Mark strings for translation.
OFIRMIF2.cpp: Mark strings for translation.
OFIRMIF3.cpp: Mark strings for translation.
OF_BASE.cpp: Mark strings for translation.
OF_CAMP.cpp: Mark strings for translation.
OF_FACT.cpp: Mark strings for translation.
OF_HARB.cpp: Mark strings for translation.
OF_INN.cpp: Mark strings for translation.
OF_MARK.cpp: Mark strings for translation.
OF_MINE.cpp: Mark strings for translation.
OF_MONS.cpp: Mark strings for translation.
OF_RESE.cpp: Mark strings for translation.
OF_WAR.cpp: Mark strings for translation.