title: Can sinon stub withArgs match some but not all arguments
body: <p>I have a function I am stubbing that gets called with multiple arguments. I want to check <strong>just the first argument</strong>. The rest are callback function, so I want to leave them alone. Thus, I might have the following 2 calls, using ajax as an example:</p>
  
  <pre><code>method.get = sinon.stub();
  method.get(25,function(){/* success callback */},function(){/* error callback */});         
  method.get(10,function(){/* success callback */},function(){/* error callback */});
  </code></pre>
  
  <p>I cannot use <code>method.get.calls...</code> because then it doesn't differentiate between the first one <code>get(25)</code> and the second <code>get(10)</code>. But if I use <code>method.get.withArgs(25).calls...</code> then it does not match either, because <code>withArgs()</code> matches <strong>all</strong> arguments, which this does not (and never could, with callbacks like that).</p>
  
  <p>How do I get sinon stubs to check and set responses based on just the 1st arg?</p>