// This is something like n^2 worst-case.
//
// []string must be sorted
func diffStrings(new, old []string) (added, removed []string) {
Add:
	for _, x := range new {
		for _, y := range old {
			if x == y {
				continue Add
			}
		}
		added = append(added, x)
	}
Rem:
	for _, x := range old {
		for _, y := range new {
			if x == y {
				continue Rem
			}
		}
		removed = append(removed, x)
	}

	return added, removed
}