>> It would be nice to remove the need to know the index at all.
>
>Does this look OK?  The configure script would need to change to fit in.

This looks very much like one of the ideas I had.
I was thinking though of shifting the custom entry to the end
to avoid the need to redefine the others - would just look neater.

Also I was thinking of renaming _BASENAME_DEFSHELL to CUSTOM_DEFSHELL ?
but DEFSHELL_NAME is fine.

Thanks
--sjg