typing: make `vfs.isfileorlink_checkdir()` path arg required...
typing: make `vfs.isfileorlink_checkdir()` path arg required
The only caller to this is `merge._checkunknownfile()`, which supplies a value.
That's good, because `util.localpath()` immediately uses the value to call a
method on it on Windows. The posix implementation returns the value unaltered,
but then `pathutil.finddirs_rev_noroot()` would have exploded.