Validate sets after, rather than before, legality enforcement is perform...

...ed.

This gets rid of the need of listing all the mega-evos as well when banning a pokémon.
It also prevents the use of Meloetta in GBU formats by crafting a Meloetta-Pirouette (not specifically banned) with Relic Song, which used to be changed to the base forme, thus by-passing the ban.