remove_root argument of Augment.augment() not considered when loading from cache

[hagenw]

The remove_root argument influences how the exact file path looks in the returned augmented index (and also where the augmented files are stored). When auglib.Augment.augment() can find a matching augmentation in the cache it returns the index for that augmentation, and does not consider remove_root. On one hand, this is a feature as it does not have to run the augmentation again, when only the path should change. On the other hand, it might break code that follows and expects that the file path looks different.

Not sure yet, how we can improve the current behavior.