fixed some warning under Ubuntu in gpu module

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

@@ -1134,8 +1134,8 @@ namespace cv
             int nbins;
             double win_sigma;
             double threshold_L2hys;
-            int nlevels;
             bool gamma_correction;
+            int nlevels;
 
         protected:
             void computeBlockHistograms(const GpuMat& img);

modules/gpu/src/match_template.cpp

@@ -269,7 +269,7 @@ void cv::gpu::matchTemplate(const GpuMat& image, const GpuMat& templ, GpuMat& re
     static const Caller callers32F[] = { ::matchTemplate_32F_SQDIFF, 0,
                                          ::matchTemplate_32F_CCORR, 0, 0, 0 };
 
-    const Caller* callers;
+    const Caller* callers = 0;
     switch (image.type())
     {
     case CV_8U: callers = callers8U; break;

modules/gpu/src/mssegmentation.cpp

@@ -69,8 +69,8 @@ public:
     vector<int> rank;
     vector<int> size;
 private:
-    DjSets(const DjSets&) {}
-    DjSets operator =(const DjSets&) {}
+    DjSets(const DjSets&);
+    void operator =(const DjSets&);
 };