ubuntu下安装opencv，cmake出错，解决方法

错误原因：
Make Error at 3rdparty/ippicv/downloader.cmake:75 (message):
  ICV: Failed to download ICV package: ippicv_linux_20140513.tgz.
  Status=28;"Timeout was reached"
Call Stack (most recent call first):
  3rdparty/ippicv/downloader.cmake:108 (_icv_downloader)
  cmake/OpenCVFindIPP.cmake:212 (include)
  cmake/OpenCVFindLibsPerf.cmake:12 (include)
  CMakeList错误原因：
Make Error at 3rdparty/ippicv/downloader.