Build error

With a fresh clone of ol3 I get the following error when running `build.py build`:

```
2013-03-06 15:14:56,415 build/ol-simple.js: java -jar bin/plovr-eba786b34df9.jar build build/ol-simple.json
Exception in thread "main" java.lang.RuntimeException: java.io.FileNotFoundException: /home/elemoine/public_html/openlayers/ol3_sample_app/ol3/build/../build/src/internal/src/requireall.js (No such file or directory)
```

A target dependency is probably missing.