block-creeper-block-damage does not protect armor stands

WORLDGUARD-3345 - Reported by RoyCurtis

With this protection config on, when a creeper explodes near armor stands it destroys them. Ideally, it should not do this as armor stands should be considered "blocks" (even though they are actually entities).

Reproduction:

* In WorldGuard config.yml, set "block-creeper-block-damage" under "mobs" to true
* /wg reload
* Place armor stands ( http://i.imgur.com/yL1nJFZ.png )
* Summon a creeper ( http://i.imgur.com/DtNdFRj.png ) and ensure you are in Survival mode
* Cause creeper to explode near stands; observe they disappear and drop any items held