Sets released: Guildpact, Dissension, Coldsnap, Time Spiral

Major stuff:

   - Coldsnap changed the 'snow-covered' supertype to 'snow' and expanded
   its use to nonland permanents.
   - Time Spiral introduced a rule to make +1/+1 and -1/-1 counters on
   a permanent disappear in pairs.
   - With the online release of Mirage block cards, the rules for phasing
   were updated.  Phasing out no longer triggers leaves play abilities.
   - Time Spiral introduced suspend, a way of playing a card for less
   mana by having it resolve some turns in the future.
   - Time Spiral introduced split second, an ability that prevents
   players from responding to the spell that it's on.  The flavour is
   similar to that of the pre-6th Edition interrupts.