drop exec permissions on setup.py
setup: remove unused imports and bzr compat
add arm64 and remove ppc-macos and x86-fbsd from the default arch list
minor spelling fix
add git-2 eclass to deprecation list
lint: whitespace, indentation, and pep8 fixes
respect stable forcing and masking settings for stable profile checks

Specifically take into account the settings in
use.stable.mask/package.use.stable.mask and
use.stable.force/package.use.stable.force.