first draft
Merge remote-tracking branch 'upstream/develop' into ebuild_enhanced

Conflicts:
	salt/states/portage_config.py
some fixes
merge fix
other merge fix
added check_extra_requirements function
check_extra_requirements documentation
some fixes
fixes
doc fix
overlay->repository
Merge pull request #5824 from faust/ebuild_enhanced

pkg.installed support for USE flags, overlay and keyword accept