WRaster: Create header for i18n helper functions

This patch is just adding a single header, but because it also modifies
all the C files to add the #include, it was made as a patch on its own to
ease review.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

wrlib/load_gif.c

@@ -30,6 +30,8 @@
 
 #include "wraster.h"
 #include "imgformat.h"
+#include "wr_i18n.h"
+
 
 static int InterlacedOffset[] = { 0, 4, 2, 1 };
 static int InterlacedJumps[] = { 8, 8, 4, 2 };