Move the discussion about CVSup out of the cutting-edge chapter and into
the "Obtaining FreeBSD" appendix.

This is a straight cut-n-paste of the affected information. However, in
its original location it was "<sect 2>", now it's "<sect1>", so all the
sectional elements have to upgraded by one.

A few references to "cvsup" as a link target were updated to "mirrors-cvsup"
as well.

Still based on work submitted by Eric Ogren, just broken down a little more.