Don't overwrite manifest with utils.sh
clean up after env_file if it's still open.
Add sentinel export to conditionally source .env from .rc
Make path_prepend a little more self-explanatory.
Only inject into config files that exist, and avoid repetitious includes.
Make the tests work.

Some random authentication test is still failing for me,
but I didn't touch that area, so I'll assume it's a brittle test.