[Mimedefang] problem with configure script?

[Anthony Giggins]

If you run the configure script once then install either File::Scan or Nai
then re-run the configure script the changes are not picked up. Even a make
clean does not fix this the easiest way I've found to fix this is the remove
the source directory and extract the archive again. I'm sure you could just
remove one of the config files but shouldn't make clean do this for you.