that's different from isModified. The isModified() method can be put to the WorkingTreeIterator. But this method writes to the WorkingTree and that's not what WorkingTreeIterator is intendet for, or? So, for know, as I would really like to a first merge out I move this method to the DirCacheCheckout class, knowing that we need a better place for it.
One problem I faced here: we do have an abstraction to access the WorkTree when walking (reading) on it. Applications could use non-filesystem working-trees in that case. But we don't have an working-tree abstraction which allows to create/update/delete files. Do we need it?
I was trying out a first attempt to have WorkingTreeWriters and one implementation for it, but it grew big enough that I decided I would like seperate this issue from the important merge.