title: RGB2BGR option disappeared from cvtColor
body: <p>I'm trying to compile my code with opencv 3.0.0 (that worked with previous opencv versions)<br>
      cvtColor(img, img, CV_RGB2BGR);<br>
  and get compilation error<br>
     ‘CV_RGB2BGR’ was not declared in this scope<br>
  The option also does not exist in the documentation 
    </p>
  
  <p>How can I get the same functionality (RGB2BGR) with the new version?</p>