Add PointLocator testing to MixedDimensionMeshTest
Add PointLocator testing to MixedDimensionMeshTest

We'll do more with this later, but for now, setting this up to make
sure we don't muck up the behavior of PointLocator as the API gets
adjusted to support mixed dimension meshes.

Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh