Move Cwd and List-Util: UNIX followup

the previous commit worked on win32; this commit makes it work under UNIX
too.

Basically Configure determines a list of "logical" extension names
such as "IPC/SysV",  based on physical dirs under cpan/ etc such as
"IPC-SysV".

In this case, keep the original logical names "Cwd" and "List/Util",
even though the physical paths have been changed to "PathTools" and
"Scalar/List/Utils".