- mirrors.yaml now uses dict order for precedence, instead of lists of
dicts.
- spack.cmd now specifies default scope for add/remove and for list
with `default_modify_scope` and `default_list_scope`.
- commands that only read or list default to all scopes (merged)
- commands that modify configs modify user scope (highest
precedence) by default
- These vars are used in setup_paraser for mirror/repo/compiler.
- Spack's argparse supports aliases now.
- added 'rm' alias for `spack [repo|compiler|mirror] remove`
b02faf5641