git simple alias with pipes and multiple arguments doesn't work.

e.g:

```
$> git dsf --cached test/
fatal: ambiguous argument '@$': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'
```

Instead we can use bash function to make the alias work with pipes and all.
