Nick, you are right about sys.exit().  I did to much C programming 
lately and forgot that sys.exit() does not exit. :-)

I understood your comment as saying that 'importer' points to a valid 
importer.  Now I understand that with the present state of the code, 
that would only be the case when running a zip file.  Now it all makes 
sense.

I still wonder if the case of a bona fide importer could be handled 
without a sys.path mutating trick by simply calling importer-
>find_module.