events: speed up .removeAllListeners()

lib/events.js

@@ -239,6 +239,17 @@ EventEmitter.prototype.removeListener = function(type, listener) {
 EventEmitter.prototype.removeAllListeners = function(type) {
   if (!this._events) return this;
 
+  // fast path
+  if (!this._events.removeListener) {
+    if (arguments.length === 0) {
+      this._events = {};
+    } else if (type && this._events && this._events[type]) {
+      this._events[type] = null;
+    }
+    return this;
+  }
+
+  // slow(ish) path, emit 'removeListener' events for all removals
   if (arguments.length === 0) {
     for (var key in this._events) {
       if (key === 'removeListener') continue;