Annual simplification drive:

1. DISTFILE is gone and replaced by DISTFILES, which can contain one or more file specifications.
2. MASTER_SITE created, which points to the distfiles directory on freebsd.cdrom.com (which I'll set up in a moment).
3. HOME_LOCATION is now simply a hint, and is never directly used except to inform the user when ncftp unable to transfer a file from MASTER_SITE.
4. ncftp is now assumed to live somewhere in the path, in preparation for Andrew bringing it in on a more permanant basis.
5. XMKMF defined - it was not before.

Thanks to Andrew (ache) for many helpful suggestions.