title: OpenCV 3.0.0 "configure" fails, ffmpeg not downloaded
body: <p>I get the following error when trying to configure OpenCV using CMAKE on windows:</p>
  
  <pre><code>CMake Warning at cmake/OpenCVUtils.cmake:865 (message):
  Download: Local copy of opencv_ffmpeg.dll has invalid MD5 hash:
  d41d8cd98f00b204e9800998ecf8427e (expected:
  89c783eee1c47bfc733f08334ec2e31c)
  
  Call Stack (most recent call first):
  3rdparty/ffmpeg/ffmpeg.cmake:10 (ocv_download)
  cmake/OpenCVFindLibsVideo.cmake:193 (include)
  CMakeLists.txt:527 (include)
  
  
  Downloading opencv_ffmpeg.dll...
  CMake Error at cmake/OpenCVUtils.cmake:888 (file):
  file DOWNLOAD MD5 mismatch
  
  for file: [C:/research/opencv300/sources/3rdparty/ffmpeg/downloads/89c783eee1c47bfc733f08334ec2e31c/opencv_ffmpeg.dll]
  expected MD5 sum: [89c783eee1c47bfc733f08334ec2e31c]
  actual MD5 sum: [d41d8cd98f00b204e9800998ecf8427e]
  
  Call Stack (most recent call first):
  3rdparty/ffmpeg/ffmpeg.cmake:10 (ocv_download)
  cmake/OpenCVFindLibsVideo.cmake:193 (include)
  CMakeLists.txt:527 (include)
  
  
  CMake Error at cmake/OpenCVUtils.cmake:892 (message):
  Failed to download opencv_ffmpeg.dll.  Status=1;"unsupported protocol"
  Call Stack (most recent call first):
  3rdparty/ffmpeg/ffmpeg.cmake:10 (ocv_download)
  cmake/OpenCVFindLibsVideo.cmake:193 (include)
  CMakeLists.txt:527 (include)
  
  
  Configuring incomplete, errors occurred!
  </code></pre>
  
  <p>I tried downloading opencv_ffmpeg.dll manually, but the configure process didn't work.</p>
  
  <p>Can you help me, how to fix that?</p>