1.执行 git pull 的时候，出现 如下 错误：
If no other git process is currently running, this probably means a
git process crashed in this repository earlier. Make sure no other git
process is running and remove the file manually to continue.
解决方法：
rm -f ./.git/index.lock
原文：http://my.oschina.net/honeyming/blog/343473