Issue #16957: shutil.which() no longer searches a bare file name in the
current directory on Unix and no longer searches a relative file path with
a directory part in PATH directories.  Patch by Thomas Kluyver.
Issue #16957: shutil.which() no longer searches a bare file name in the
current directory on Unix and no longer searches a relative file path with
a directory part in PATH directories.  Patch by Thomas Kluyver.