title: Calling different callbacks for stub on firstcall and second call
body: <p>I'm looking for a way in sinon to call different functions in first and second call to the stub method.</p>
  <p>Here is an example:</p>
  <pre class="lang-js prettyprint-override"><code>var func1 = function(connectionPolicy, requestOptions, callback) {
    callback({code: 403});
  }
  
  var func2 = function(connectionPolicy, requestOptions, callback) {
    callback(undefined);
  }
  
  var stub = sinon.stub();
  
  // Something of this form
  stub.onCall(0) = func1;
  stub.onCall(1) = func2;
  
  request.createRequestObjectStub = stub;
  </code></pre>
  <p>So that when <code>request.createrequestObjectStub</code> gets called internally(when calling a public API), I see this behavior.</p>
  <ul>
  <li>Sinon version: 1.17.4</li>
  <li>Environment: Node JS</li>
  </ul>