Specify explicit format for fprintf()

The second argument in fprintf() needs to be a format, not
the (random) string that is actually filled in. Otherwise, the
behaviour is unexpected/undefined when the string contains a percent
sign.

sys/memdbg/memlog.c

@@ -133,7 +133,7 @@ char	*message;
 	    "------", number++, "------");
 
 	/* Output message. */
-	fprintf (fp, message);
+	fprintf (fp, "%s", message);
 	fprintf (fp, "\n");
 
 	fflush (fp);