Improve socket error handling so that a socket error isn't an

automatic fatalbox(). Instead, the error is passed to the receiver
routine, which can decide just how fatal the problem really is.

[originally from svn r894]

telnet.c

@@ -461,6 +461,11 @@ static void do_telnet_read (char *buf, int len) {
 }
 
 static int telnet_receive(Socket s, int urgent, char *data, int len) {
+    if (urgent==3) {
+        /* A socket error has occurred. */
+        connection_fatal(data);
+        len = 0;
+    }
     if (!len) {
 	/* Connection has closed. */
 	sk_close(s);