rename's return value is buggered.

[shadowcat-mst]

Since it just passes on the new name when constructing the return value, if you give a relative path to rename to, with an absolute invocant, the rename works, but you get back a relative object, not an absolute one. When the cwd is not the same as the directory of the absolute path you called rename on, this behaviour is made of urine and may impact our ability to locate cats.