[Feature request] option to fail if libraries source are dirty

[tanja84dk]

I have thought a lot about if it wouldn't be a great idea with a option to make the build failing if a source is corrupt/dirty.

It could even be a environment variable just like use local cache

The reason is specially to make it easier to catch a corrupt cache in automation ( like for me its Jenkins there is running nightly tests/build )

I do though feel it would be best that it is a opt in to use just like the use local cache