Add ocl's good features to track implementation.

Additional notes with this commit:
1. Add cornerHarris_dxdy and cornerMinEigenVal_dxdy to get
the interim dx and dy output of Sobel operator;
2. Add minMax_buf to allow user to reuse buffers in minMax;
3. Fix an error when either min or max pointer fed into minMax is NULL;
4. Corner sorter temporarily uses C++ STL's quick sort. A parallel
 selection sort in OpneCL is contained in the implementation but disabled
due to poor performance at the moment.
5. Accuracy test for ocl gfft.

modules/ocl/src/mcwutil.cpp

@@ -156,7 +156,7 @@ namespace cv
                 format.image_channel_order     = CL_RGBA;
                 break;
             default:
-                CV_Error(-1, "Image forma is not supported");
+                CV_Error(-1, "Image format is not supported");
                 break;
             }
 #ifdef CL_VERSION_1_2
@@ -225,6 +225,11 @@ namespace cv
             openCLSafeCall(err);
             return texture;
         }
+        Ptr<TextureCL> bindTexturePtr(const oclMat &mat)
+        {
+            return Ptr<TextureCL>(new TextureCL(bindTexture(mat), mat.rows, mat.cols, mat.type()));
+        }
+
         void releaseTexture(cl_mem& texture)
         {
             openCLFree(texture);