[gentoo-portage-dev] support multiple eclass variants (aka "unstable eclasses")

[Michael Haubenwallner]

Hello fellow Portage developers,

attached portage patch draft aims to allow for easy distributing eclasses to be tested by
multiple tinderboxes on various architectures, without being active for normal installs.

Usage is to have in make.conf (or profile): PORTAGE_ECLASS_VARIANTS="testing"
and for the eclass: to live in tree-or-overlay/eclass/testing/

Thoughts? (even for var-naming, manpage yes/no/wording, ...)

Thank you!
/haubi/