opencv3.1.0添加opencv_contrib失败——ocv_download

CMake Error at /Users/Documents/opencv/source/opencv-3.2.0/cmake/OpenCVUtils.cmake:1045 (file):
file DOWNLOAD cannot open file for write.
Call Stack (most recent call first):
/Users/Documents/opencv/source/opencv_contrib-master/modules/dnn/cmake/OpenCVFindLibProtobuf.cmake:32 (ocv_download)
/Users/Documents/opencv/source/opencv_contrib-master/modules/dnn/CMakeLists.txt:5 (include)

CMake Error at /Users/Documents/opencv/source/opencv-3.2.0/cmake/OpenCVUtils.cmake:1049 (message):
Failed to download . Status=
Call Stack (most recent call first):
/Users/Documents/opencv/source/opencv_contrib-master/modules/dnn/cmake/OpenCVFindLibProtobuf.cmake:32 (ocv_download)
/Users/Documents/opencv/source/opencv_contrib-master/modules/dnn/CMakeLists.txt:5 (include)
在用cmake编译opencv3.1以及配套的opencv_contrib模块的时候，遇到了以上错误，解决办法是在错误提示的.cmake文件中找到FILENAME这个词，然后用PACKAGE替换之即可。记录下来对自己是一个提醒，也许也有人看到这个会少走些弯路。

参考：https://github.com/opencv/opencv_contrib/issues/1100

            http://stackoverflow.com/questions/43081022/ubuntu-opencv-not-compiling