git-pull

常用形式

git pull origin +<src>:<des>
git pull origin <src>:<des>
git pull origin <src>（src-->FETCH_HEAD）
    The ref names and their object names of fetched refs are stored in .git/FETCH_HEAD

fetch的缺省行为

缺少<refspec>时：
    1 branch.<name>.fetch
    2 remote.<name>.fetch
    3 branch.<name>.merge
    4 远程的HEAD