WORLDGUARD-2613 - Reported by Gamerguy14

I was working on making my archery plugin work with WorldGuard. I was able to make all protections work except for explosion protection. After digging through some of the Craftbukkit source, and some of WorldGuard's source, I noticed that if an explosion has a non-null entity, and isn't an entity that usually explodes (e.g. Creeper, Fireball), there is no check on the explosion. The only check for "Other Explosions" is done when the entity is null. This is problematic because plugins causing other entities to explode will create explosions that violate protections.