demos: better error message for overlay.c, see bug 20055
diff --git a/progs/xdemos/overlay.c b/progs/xdemos/overlay.c
index 4c425b6..758f85c 100644
--- a/progs/xdemos/overlay.c
+++ b/progs/xdemos/overlay.c
@@ -165,7 +165,8 @@
          /* XXX setup the colormap entries! */
       }
       else {
-         printf("Error: couldn't get an overlay visual!\n");
+         printf("Couldn't get an overlay visual.\n");
+         printf("Your hardware probably doesn't support framebuffer overlay planes.\n");
          exit(1);
       }
    }