title: OpenCV: ‘AlgorithmInfo’ does not name a type while building opencv_contrib
body: <p>I am getting the following error while trying to build opencv with the contrib module</p>
  
  <pre><code>/opencv/opencv_contrib/modules/tracking/include/opencv2/tracking/tracker.hpp:577:11: error: ‘AlgorithmInfo’ does not name a type
  </code></pre>
  
  <p>The code is latest and pulled just now.
  After adding a forward declaration <code>class AlgorithmInfo;</code> to the file tracker.hpp that particular error is gone but I am getting other '‘AlgorithmInfo’ does not name a type' errors in other files. Probably AlgorithmInfo is not getting included somehow. Any ideas? </p>
  
  <p>Investigation: </p>
  
  <ol>
  <li><p>After grepping AlgorithmInfo I found that there is no defination of AlgorithmInfo in the code base.</p></li>
  <li><p>Comparing to the previous version of code I found AlgorithmInfo is defined at opencv2/core.hpp line 3006. But in the latest code, it is <strong>not present</strong> there at all!</p></li>
  </ol>