[gentoo-catalyst] [PATCH] Use Portage's make.conf parser, allow user-specified extra bind mount points, allow absolute profile paths

[Charles Duffy]

Attached is a collection of enhancements I'm using in my local catalyst
installation. In particular:

 - Uses the make.conf parser from portage_utils. This handles source
directives, multi-line constants, and other goodness the catalyst one
doesn't.
 - Adds a new directive, "extra_mounts", allows user-specified bind
mount points. If for some reason an advanced user who's doing funky
things wants extra bind mounts into the build region, this permits it.
 - Allow absolute profile paths. Necessary for folks using custom
profiles not within /usr/portage/profiles. (In my case, that profile is
coming off a network filesystem for which a bind mount is set up via the
extra_mounts directive).

If 'yall want me to split patch this out into multiple pieces, I'd be
glad to do so.