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/convolve.c

@@ -25,7 +25,10 @@
 #include <stdio.h>
 #include <string.h>
 #include <X11/Xlib.h>
+
 #include "wraster.h"
+#include "wr_i18n.h"
+
 
 /*
  *----------------------------------------------------------------------