partially recovered binary compatibility (ticket #2415)

modules/contrib/include/opencv2/contrib/detection_based_tracker.hpp

@@ -7,8 +7,6 @@
 
 #include <vector>
 
-namespace cv
-{
 class DetectionBasedTracker
 {
     public:
@@ -169,5 +167,10 @@ class DetectionBasedTracker
         cv::Rect calcTrackedObjectPositionToShow(int i, ObjectStatus& status) const;
         void detectInRegion(const cv::Mat& img, const cv::Rect& r, std::vector<cv::Rect>& detectedObjectsInRegions);
 };
+
+namespace cv
+{
+    typedef ::DetectionBasedTracker DetectionBasedTracker;
+    
 } //end of cv namespace
 #endif