Multipart Entity API is only useable for Living Entities

[Daomephsta]

Multipart entities are not implicitly alive, in my case the multipart entity is a boat. The only field of EntityLiving that is used is EntityLivingBase#renderYawOffset. I propose that this could be replaced solved by handling the child entities the same way the vanilla boat handles passengers(see EntityBoat#applyYawToEntity()).