- `spack edit` previously used `spack.util.executable` `Executable` objects,
and didn't `exec` the editor like you'd expect it to
- This meant that Spack was still running while your editor was, and
stdout/stdin were being set up in weird ways
- e.g. on macOS, if you call `spack edit` with `EDITOR` set to the
builtin `emacs` command, then type `Ctrl-g`, the whole thing dies with
a `==> Error: Keyboard interrupt`
- Fix all this by changing spack.util.editor to use `os.execv` instead of
Spack's `Executable` object
0aed3bcea6