Add .env awareness, distinct from .rc
Make env formula's exclusion of keys more graceful.
Use prepend_path function from utils.sh to add path-related env vars.
Provide utils.sh, dispensing with weird env var.
Perforce formula should add to env, not rc.
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.
Namespace the path utility function, and ensure .env file is present before sourcing in .rc.
Merge branch 'master' into split_env_rc

Conflicts:
	sprinter/environment.py
Just warn about sourcing rc from env file instead of removing it.
Use 'with' idiom when writing utils.sh
.rc always sources .env, and does not export sentinel.
Private method already called in destructive_clear().
Laying groundwork for triune environment injection.
That'll teach me to push without running tests.
Only complain about rc sourced from env when installing an environment.