call EventEmmiter constructor on native Connection

this allows to preserve an active domain on switches in libpq

lib/native/index.js

@@ -155,6 +155,7 @@ Connection.prototype.sendCopyFail = function(msg) {
 var clientBuilder = function(config) {
   config = config || {};
   var connection = new Connection();
+  EventEmitter.call(connection);
   connection._queryQueue = [];
   connection._namedQueries = {};
   connection._activeQuery = null;