TTY: printer better diagnostics

.tell when a line is not initialized
.don't print when a request has failed, we use error codes for that

drivers/tty/rs232.c

@@ -444,6 +444,8 @@ void rs_init(tty_t *tp)
    * for all requests on it from userland. (The kernel will use it.)
    */
   if(env_get_param(SERVARNAME, l, sizeof(l)-1) == OK && atoi(l) == line) {
+	printf("TTY: not initializing rs232 line %d (in use by kernel)\n",
+		line);
 	return;
   }
 

drivers/tty/tty.c

@@ -258,8 +258,6 @@ int main(void)
 
 	/* If the device doesn't exist or is not configured return ENXIO. */
 	if (tp == NULL || ! tty_active(tp)) {
-		printf("Warning, TTY got illegal request %d from %d\n",
-			tty_mess.m_type, tty_mess.m_source);
 		if (tty_mess.m_source != LOG_PROC_NR)
 		{
 			tty_reply(TASK_REPLY, tty_mess.m_source,