debugger: print port number when connecting to debuggee

To improve troubleshooting of debugger problems in the future,
the debugger repl now prints the port it is connecting to.

lib/_debugger.js

@@ -1702,7 +1702,7 @@ Interface.prototype.trySpawn = function(cb) {
   }
 
   setTimeout(function() {
-    self.print('connecting..', true);
+    self.print('connecting to port ' + port + '..', true);
     attemptConnect();
   }, 50);
 };