Before this change, renaming a file or directory through a name that
matched it only by ignoring case (`--vfs-case-insensitive`, the default on
macOS and Windows) or Unicode normalization left its old entry in the
parent directory. The item was listed twice, once under its new name and
once under the old key, and the old name still resolved to it until the
directory cache expired. `Dir.Rename` removed the parent's entry under the
name it was given rather than the item's real name. For a directory
renamed within its own parent, this was masked until `36ce1a28f`, which
removed a second deletion in `Dir.rename`.
After this change, `Dir.Rename` removes the entry under the item's real
name. The issue was discovered on the bisync integration tests.
nielash
694dae2ed7