Add a new function, fspath The function, given a relative filename and a root, returns the filename modified to use the case actually stored in the filesystem (or None if the file does not exist). The returned name is relative to the root, but retains the path separators used in the input path. (This is not strictly necessary, but retaining the path separators minimises misleading test suite failures). A win32-specific implementation (using win32api.FindFiles) is possible, but it has not been implemented as testing seems to demonstrate that the win32-specific code is not significantly faster (thanks to the caching of results in the generic code).