[Import-SIG] PEP 420 issue: extend_path

["Martin v. Löwis"]

> Why would it break existing finders? finder_module() would either return
> a loader, or a dedicated object (or None).

That wouldn't fix the issue at hand: callers of find_module that either 
expect None or a loader would still break when they get the dedicated
object.

> Returning a string is completely non-obvious to the caller (who may not
> know about namespace packages or their precise implementation in PEP
> 420).

For the issue at hand, it makes no difference whether it's a string or
a dedicated object.

Regards,
Martin