Revert "fixed compilation error because of DetectionBasedTracker"

This reverts commit 9b8c47399a.

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

@@ -27,7 +27,6 @@ class DetectionBasedTracker
                     minNeighbours(2),
                     scaleFactor(1.1f)
                 {}
-                virtual ~IDetector() {}
 
                 virtual void detect(const cv::Mat& image, std::vector<cv::Rect>& objects) = 0;
 
@@ -63,6 +62,7 @@ class DetectionBasedTracker
                 {
                     minNeighbours = value;
                 }
+                virtual ~IDetector() {}
 
             protected:
                 cv::Size minObjSize;
@@ -107,6 +107,7 @@ class DetectionBasedTracker
         };
         virtual void getObjects(std::vector<ExtObject>& result) const;
 
+
         virtual int addObject(const cv::Rect& location); //returns id of the new object
 
     protected:
@@ -169,7 +170,7 @@ class DetectionBasedTracker
 
 namespace cv
 {
-    using ::DetectionBasedTracker;
+    typedef ::DetectionBasedTracker DetectionBasedTracker;
+    
 } //end of cv namespace
-
 #endif