title: Ivy dependency with changing="true" always downloads artifacts, even not changed
body: <p>According to Ivy documentation dependency with <strong>changing="true"</strong> means the module can change even if the revision is the same. This is useful especially for integration.</p>
  
  <p>Now, I expect the system is smart enough so it does not download artifacts every time.
  It can compare, for example, <strong>"publication"</strong> timestamps in ivy.xml and download (and cache) only if necessary.</p>
  
  <p>But this is not the case if the dependency has <strong>rev="latest.integration"</strong>. I see it downloads artifacts every time and I'm sure they were not changed. If I change "rev" to some exact revision, then it works as expected.</p>
  
  <p>Is this expected behavior and do I have any chance to make it work with "latest.integration"?</p>
  
  <p>I use Ivy 2.2.0.</p>