Workaround fix for players who have a passenger (pet riding their head or whatever) being able to bypass borders. This is due to a CraftBukkit issue (bug really, but whatever) where all teleportation fails silently if the entity attempted to be teleported has a rider/passenger.

Normally players can't have anything riding them, but various plugins make that possible for pets or similar, as unwise as that may currently be with the CraftBukkit teleportation problems outlined above.

I finally set aside some time to add and test this workaround out using EchoPet to make sure it actually works.