incorrect export of "conflicting" renames

[Jonas]

mv a t
mv b a
mv t b

---

The tree changed object will only report a->b and b->a
i.e a "summary" of what has happened.

however, doing this immediate is not possible, as then only one of the files will remain
mv a b
mv b a

---

Solution is to detect the conflict, and introduce a temporary rename

[Philipp Wolfer (phw)]

I had a similar problem with a deletion of a directory followed by a rename of a file inside the directory. The operations were like this:

D a
R a/b b

Switching those lines in the export stream solves the problem.