COMMITTED: SE_InterruptCasting

[Caryatis]

Kinda minor one but seemed easy to bang out, used in the bard AA Cacophony (http://lucy.allakhazam.com/spell.html?id=11215&source=Live) and some late expansion AEs.

code...
spell effects.cpp - line 2818 - add this
case SE_InterruptCasting:

spell effects.cpp - line 3288 - add this
case SE_InterruptCasting:
{
if(IsCasting())
{
if(MakeRandomInt(0, 100) <= spells[spell_id].base[i])
{
InterruptSpell();
}
}
break;
}