clean code; fix problems in documentation

modules/gpu/include/opencv2/gpu/gpu.hpp

@@ -1586,7 +1586,7 @@ public:
     //    There non zero value mean that detector should be executed in this point.
     // Param mask is an output mask
     // Param stream is stream is a high-level CUDA stream abstraction used for asynchronous execution
-    void genRoi(InputArray roi, OutputArray mask, Stream& stream = Stream::Null()) const;
+    virtual void genRoi(InputArray roi, OutputArray mask, Stream& stream = Stream::Null()) const;
 
 private:
 
@@ -1600,6 +1600,8 @@ private:
     int rejCriteria;
 };
 
+CV_EXPORTS bool initModule_gpu(void);
+
 ////////////////////////////////// SURF //////////////////////////////////////////
 
 class CV_EXPORTS SURF_GPU