WRaster: Improve error messages to provide useful information to user

The original error messages tended to be a bit sparse, now they try to be
a little bit more helpful, and translatable in user's language.

In xutil.c:122, took opportunity fix a problem because calling 'perror'
after other function which are likely to have changed the errno is likely
to provide a wrong error string.

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

wrlib/context.c

@@ -407,7 +407,8 @@ static Bool setupPseudoColorColormap(RContext * context)
 			}
 
 			if (theMap < 0) {
-				puts("wrlib: no std cmap found");
+				fprintf(stderr, _("wrlib: no standard colormap found for visual 0x%lX\n"),
+				        context->visual->visualid);
 			}
 
 			if (theMap >= 0 && allocateStandardPseudoColor(context, &maps[theMap])) {