title: Calling original function from Sinon.js Stub
body: <p>I'm trying to intercept a call with Sinon.js so I can do some logging and then execute the original call.  I don't see a way to do this with sinon.spy(), but I think I can do it with sinon.stub().</p>
  
  <p>I provided a custom function:</p>
  
  <pre><code>sinon.stub(servicecore.ServiceWrapper.prototype, '_invoke', function(method, name, body, headers, callback) {
      console.log('---- ServiceWrapper._invoke called! ----');
  
  // How do I call the original function?
  
  });
  </code></pre>
  
  <p>The problem I have is executing the original function, so my application behaves the same.  Any idea?</p>