Add deprecation message for http.Client

lib/http.js

@@ -1485,6 +1485,9 @@ exports._connectionListener = connectionListener;
 // Legacy Interface
 
 function Client(port, host) {
+  // TODO http.Client can be removed in v0.9. Until then leave this message.
+  console.trace('http.Client is a legacy interface and will be removed in ' +
+                'the near future. Do not use it.');
   host = host || 'localhost';
   port = port || 80;
   this.host = host;