Major rework of headers inclusion style Part2 on behalf of lebedev.ri (issue 1079)

rtgui/previewhandler.cc

@@ -16,9 +16,9 @@
  *  You should have received a copy of the GNU General Public License
  *  along with RawTherapee.  If not, see <http://www.gnu.org/licenses/>.
  */
-#include <previewhandler.h>
+#include "previewhandler.h"
 #include <gtkmm.h>
-#include <rtengine.h>
+#include "../rtengine/rtengine.h"
 
 using namespace rtengine;
 using namespace rtengine::procparams;