d854bf6b53
When processing an alias, rename, implication, mass update, or nuke, update the posts in parallel. This means that if we alias foo to bar, for example, then we use four processes at once to retag the posts from foo to bar. This doesn't mean that if we have two aliases in a BUR, we process both aliases in parallel. It simply means that when processing an alias, we update the posts in parallel for that alias.