title: Sinon.js calledWithExactly() dynamic number of arguments
body: <p>Let's consider the following function:</p>
  
  <pre><code>function MyClass(...);
  MyClass.prototype.funcToTest = function() {
      var args = arguments;
      ...
  }
  </code></pre>
  
  <p>I wish to be able to test with what arguments this function was called with.
  In my test I do the following:</p>
  
  <pre><code>var obj = new MyClass();
  sinon.spy(obj, 'funcToTest');
  var args = [5, 3, 8];
  MyClass.prototype.funcToTest.apply(obj, args);
  sinon.assert.calledWithExactly(obj.funcToTest, args); // Here's the problem
  </code></pre>
  
  <p>The problem is that this assert fails and I'm not sure why.ith?</p>