Zac's USERLAND guessing yields in big problems for Prefix. Prefix users

Zac's USERLAND guessing yields in big problems for Prefix.  Prefix users
/always/ have a GNU userland.  I could reliably make this the case in
portage/data.py.  In isolated-functions.sh I couldn't.  It looks strange
to me it's being set there as well.

I personally hope that USERLAND can go away some day.  Prefix could
cater for this in the current FreeBSD case, by simply having an
alternative EPREFIX for a number of packages that Portage needs (bash,
coreutils, findutils, sed, gawk ...).

svn path=/main/branches/prefix/; revision=9125