title: opencv2/calib3d.hpp : No suh file or directory (How to link opencv to qt correcttly)
body: <p>I installed opencv 3.4.0-dev and I want to use it with QT.
  In the .pro I added :</p>
  
  <pre><code>LIBS += -L/usr/local/lib -lopencv_core -lopencv_imgcodecs -lopencv_highgui -lopencv_calib3d
  INCLUDEPATH += /usr/local/include/opencv
  </code></pre>
  
  <p>but i still have the error
  <code>opencv2/calib3d.hpp : No such file or directory</code>
  (I also try with highgui, imgcedexs, core, same error)</p>
  
  <p>Any idea to fix it ? 
  Thank you in advance.</p>