stream: make setEncoding chainable

lib/_stream_readable.js

@@ -198,6 +198,7 @@ Readable.prototype.setEncoding = function(enc) {
     StringDecoder = require('string_decoder').StringDecoder;
   this._readableState.decoder = new StringDecoder(enc);
   this._readableState.encoding = enc;
+  return this;
 };
 
 // Don't raise the hwm > 128MB

test/simple/test-stream2-set-encoding.js

@@ -359,3 +359,9 @@ test('encoding: base64', function(t) {
     t.end();
   });
 });
+
+test('chainable', function(t) {
+  var tr = new TestReader(100);
+  t.equal(tr.setEncoding('utf8'), tr);
+  t.end();
+});