Add a new 'git subtree add' command for adding subtrees from a given rev.
lrwxrwxrwx 14 git-subtree -> git-subtree.sh
-rwxr-xr-x 7444 git-subtree.sh
-rw-r--r-- 23 shellopts.sh
-rwxr-xr-x 1926 test.sh