When _expand_alias is invoked as a completer, if 'complete' is set to 'true', let _expand_alias always return 1. This is analogous to how this style behaves when _expand_alias is invoked as a widget or when the _expand completer's 'accept-exact' style is set to 'continue', which allows you to put it at the start of the 'completer' list. Additionally, tag alias expansions as 'expansions', rather than as 'aliases', to prevent aliases & alias expansion from being lumped into the same group.