stream: Override addListener as well as on

For the compatibility switch.

lib/_stream_readable.js

@@ -510,7 +510,7 @@ Readable.prototype.unpipe = function(dest) {
 // kludge for on('data', fn) consumers.  Sad.
 // This is *not* part of the new readable stream interface.
 // It is an ugly unfortunate mess of history.
-Readable.prototype.on = function(ev, fn) {
+Readable.prototype.addListener = Readable.prototype.on = function(ev, fn) {
   var res = Stream.prototype.on.call(this, ev, fn);
 
   // https://github.com/isaacs/readable-stream/issues/16