Diff not handle folders been relplace by files with same name

If you have two file Tree and call `auto diff = tree0.createDiff(tree1);` if `tree0` has a folder called `foo` and `tree1` has had that folder removed and a file added called `foo` the resulting diff will not contain info about the file.

Start at the tree0.createDiff(tree1) entry point and reproduce the case where a folder named foo is replaced by a file with the same name. Inspect the resulting diff and compare it with the expected file information. Done means the diff reports the replacement and includes the new file.

Scritto dal modello di indicizzazione a partire dal testo della issue.