tal-m

@lane: Mea culpa! I was wrong and @noamnelke is correct. The ATXs on-time status shouldn't matter for block validation, only for determining the *rewarded blocks*. Otherwise, honest parties could continue...

> Dumb, obvious question: this means we won't allow changing the signatories later, right? I.e., the set of authorized pubkeys is part of immutable state? This is also a usability...