Conversion to gettext to allow localization

This is just the first step - convert the string literals, try to catch
all the places where this isn't possible and the program needs to convert
string constants at runtime (those are the N_ macros).

Add a very rough first German localization so I can at least test what I
have done. Seriously, I have never used a localized OS, so I am certain
that I have many of the 'standard' translations wrong. Someone please take
over :-)

Major issues with this:

- right now it hardcodes the search path for the message catalog to be
  ./locale - that's of course bogus, but it works well while doing initial
  testing. Once the tooling support is there we just should use the OS
  default.

- even though de_DE defaults to ISO-8859-15 (or ISO-8859-1 - the internets
  can't seem to agree) I went with UTF-8 as that is what Gtk appears to
  want to use internally. ISO-8859-15 encoded .mo files create funny
  looking artefacts instead of Umlaute.

- no support at all in the Makefile - I was hoping someone with more
  experience in how to best set this up would contribute a good set of
  Makefile rules - likely this will help fix the first issue in that it
  will also install the .mo file(s) in the correct place(s)

  For now simply run

  msgfmt -c -o subsurface.mo deutsch.po

  to create the subsurface.mo file and then move it to
  ./locale/de_DE.UTF-8/LC_MESSAGES/subsurface.mo

  If you make changes to the sources and need to add new strings to be
  translated, this is what seems to work (again, should be tooled through
  the Makefile):

  xgettext -o subsurface-new.pot -s -k_ -kN_ --add-comments="++GETTEXT" *.c
  msgmerge -s -U po/deutsch.po subsurface-new.pot

  If you do this PLEASE do one commit that just has the new msgid as
  changes in line numbers create a TON of diff-noise. Do changes to
  translations in a SEPARATE commit.

- no testing at all on Windows or Mac
  It builds on Windows :-)

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

main.c

@@ -1,8 +1,11 @@
 /* main.c */
+#include <locale.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <time.h>
+#include <libintl.h>
+#include <glib/gi18n.h>
 
 #include "dive.h"
 #include "divelist.h"
@@ -29,17 +32,19 @@ static int sortfn(const void *_a, const void *_b)
 
 const char *weekday(int wday)
 {
-	static const char wday_array[7][4] = {
-		"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
+	static const char wday_array[7][7] = {
+		/*++GETTEXT: these are three letter days - we allow up to six code bytes */
+		N_("Sun"), N_("Mon"), N_("Tue"), N_("Wed"), N_("Thu"), N_("Fri"), N_("Sat")
 	};
 	return wday_array[wday];
 }
 
 const char *monthname(int mon)
 {
-	static const char month_array[12][4] = {
-		"Jan", "Feb", "Mar", "Apr", "May", "Jun",
-		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
+	static const char month_array[12][7] = {
+		/*++GETTEXT: these are three letter months - we allow up to six code bytes*/
+		N_("Jan"), N_("Feb"), N_("Mar"), N_("Apr"), N_("May"), N_("Jun"),
+		N_("Jul"), N_("Aug"), N_("Sep"), N_("Oct"), N_("Nov"), N_("Dec"),
 	};
 	return month_array[mon];
 }
@@ -221,6 +226,13 @@ int main(int argc, char **argv)
 	int i;
 	gboolean no_filenames = TRUE;
 
+	/* set up l18n - the search directory needs to change
+	 * so that it uses the correct system directory when
+	 * subsurface isn't run from the local directory */
+	setlocale( LC_ALL, "" );
+	bindtextdomain("subsurface", "./locale");
+	bind_textdomain_codeset("subsurface", "utf-8");
+	textdomain("subsurface");
 	output_units = SI_units;
 
 	subsurface_command_line_init(&argc, &argv);