白天git clone 下载tensorflow安装包时候网速很慢经常失败，因此可以直接在网站下载tensorflow-master.zip,解压后如果直接源码安装会出现 GIT_DISCOVERY_ACROSS_FILESYSTEM not set, fatal: You are on a branch yet to be born， didn't match any files known to git 等错误，解决方案：
解压后
cd tensorflow
git init
git remote add origin https://github.com/tensorflow/tensorflow
git fetch
经过一段时间
git checkout r1.6
显示：
swiched to a new branch r1.6
搞定