disklabel compatibility

[Charles Dickman <chd%chdickman.com@localhost>]

I have a VS4000/60 that has NetBSD 6.0.1 and I wanted to install a
different version on another partition. When I netboot an install
system for versions other than 6.0.1, disklabel doesn't recognize the
label on the disk and presents the faked label with only partition c
that covers the whole disk.

I know that there were some recent changes to allow more partions, but
this happens not only with 6.1.4, but also 5.0.1 and 2.x.

-chuck