Implemened npc special ability (43) CASTING_RESIST_DIFF which sets innate resist modifier on
ALL spells used by that NPC. Ie. 43,1,-200 will set a -200 innate resist diff, so if your npc cast
a spell that has a -10 resist modifier the final resist diff would be -210.
Merge pull request #329 from KayenEQ/Development

NPC special ability (43) CASTING_RESIST_DIFF