In case if app is installed by npm install <git tarball url> which is very comfortable thing (postinstall hooks, automatic package installation and so on) babel is unable to run over packages, e.g.
```
~/node_modules/some_app$ node-babel app.js
```
is crashing as babel do not want in node_modules directory.
relative path gives ability to check whether lib is in node_modules _relative_ to current app, so that if app is ran in node_modules by itself it will not be captured.
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