title: Compiling error cv::gpu
body: <p>I'm using OpenCV master branch (3.0.0. dev) with CUDA on Ubuntu 12.04, and trying to compile the following opencv with gpu code:</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include "opencv2/opencv.hpp"
  #include "opencv2/core.hpp"
  #include "opencv2/highgui.hpp"
  #include "opencv2/gpu/gpu.hpp"
  
  using namespace cv;
  
  int main (int argc, char* argv[])
  {
      try
      {
          cv::Mat src_host = cv::imread("file.png", CV_LOAD_IMAGE_GRAYSCALE);
          cv::gpu::GpuMat dst, src;
          src.upload(src_host);
  
          cv::gpu::threshold(src, dst, 128.0, 255.0, CV_THRESH_BINARY);
  
          cv::Mat result_host = dst;
          cv::imshow("Result", result_host);
          cv::waitKey();
      }
      catch(const cv::Exception&amp; ex)
      {
          std::cout &lt;&lt; "Error: " &lt;&lt; ex.what() &lt;&lt; std::endl;
      }
      return 0;
  }
  </code></pre>
  
  <p>The compiling command is:</p>
  
  <pre><code>g++ testgpu.cpp -o test `pkg-config --cflags --libs opencv` -lopencv_gpu
  </code></pre>
  
  <p>It has the following compiling errors:</p>
  
  <pre><code>testgpu.cpp: In function ‘int main(int, char**)’:
  testgpu.cpp:13:51: error: ‘CV_LOAD_IMAGE_GRAYSCALE’ was not declared in this scope
           cv::Mat src_host = cv::imread("file.png", CV_LOAD_IMAGE_GRAYSCALE);
                                                     ^
  testgpu.cpp:17:52: error: ‘CV_THRESH_BINARY’ was not declared in this scope
           cv::gpu::threshold(src, dst, 128.0, 255.0, CV_THRESH_BINARY);
                                                      ^
  testgpu.cpp:19:31: error: conversion from ‘cv::gpu::GpuMat’ to non-scalar type ‘cv::Mat’ requested
           cv::Mat result_host = dst;
                             ^
  </code></pre>
  
  <p>It is something wrong with the installation of OpenCV, or the API change in Opencv 3.0.0?</p>