The previous iteration, besides failing to handle leaf-only input,
was relying on splitFilePathName, which just doesn't do what's required
to incrementally build the directory tree the right way around ;).
This should more closely match mkdir -p, i.e., it will *fail* if any
part (or all of it) of the path exists but is *not* a directory.
Re #10074
NiLuJe
318a22d913