title: OCMock doesn't stub NSBundle method
body: <p>I'm using since recently OCMock for my unit testing. I need to stub the 
  <code>objectForInfoDictionaryKey:</code> method from <code>NSBundle</code>. I've done the following :</p>
  
  <pre><code>self.bundleMock = OCMClassMock([NSBundle class]);
  OCMStub([self.bundleMock objectForInfoDictionaryKey:@"GITHash"]).andReturn(@"c424242");
  ;
  </code></pre>
  
  <p>Here is the call I wanna stub :</p>
  
  <pre><code>NSString * appHashString = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"GITHash"];
  </code></pre>
  
  <p>But nothing seem to be stubbed, at runtime I still have the "correct" value.</p>
  
  <p>What did I do wrong ?</p>