null the client once end is done

lib/sequelize/connector-manager.js

@@ -38,8 +38,8 @@ ConnectorManager.prototype.query = function(sql, callee, options) {
 }
 
 ConnectorManager.prototype.disconnect = function() {
-  this.client.end(function() {})
-  this.client = null
+  var self = this
+  this.client.end(function() { self.client = null })
 }
 
 ConnectorManager.prototype.reconnect = function() {