When git invokes a hook, it passes the path to the git command used to invoke this hook via the environment varialbe '_'. We should respect this environment variable in our hooks.
<rdar://problem/105402860>
Pull request: https://github.com/WebKit/WebKit/pull/10048
This is a very bad idea, as it turns out, `_` will be `git-webkit` if `git-webkit` invokes `git`.