Show the "nuking the root" effect

Environment variables registered in variables.sh remain even on opam env
for a different switch.

Author: dra27

tests/reftests/init-scripts.unix.test

@@ -138,3 +138,8 @@ alias precmd 'eval `opam env --shell=csh --readonly`'
 # Return code 1 #
 ### test -f root/opam-init/env_hook.ps1
 # Return code 1 #
+### opam switch create fake2 --empty --root root
+### # Simulate nuking a root entirely
+### rm -rf root/fake2
+### sh locally-in-sh.sh sh -lc "opam exec --root root --switch=fake -- env" | grep -v MANPATH | grep /root/fake2/ | '=.*' -> ''
+PATH