add portage-2 profile format support

The entire repoconfig usage should be reworked to use a mapping from
something like a multikey dict (with path and repo_id as keys and
RepoConfig objects as values) encapsulated by the global config object
so we aren't creating multiple copies of RepoConfig objects.
fix doins argument checking for ebuilds using explicit "insinto /" calls

This probably wasn't discovered sooner since the root directory is the
default path for doins so most ebuilds don't explicitly set it using
insinto.
don't default to realpaths for livefs intersects

This fixes collision-protect errors when installing python packages
using newer python-exec that install into /usr/lib/python-exec which
is a symlink to /usr/lib64/python-exec on multilib amd64 systems.