Use Elem::mapping_type() for volume()
Use Elem::mapping_type() for volume()

This should give us, not the exact results with rational mapping
functions, but at least results accurate up to quadrature error.

dschwen/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,libMesh/libmesh,roystgnr/libmesh,jwpeterson/libmesh,libMesh/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,BalticPinguin/libmesh,jwpeterson/libmesh,capitalaslash/libmesh,BalticPinguin/libmesh,jwpeterson/libmesh,dschwen/libmesh,dschwen/libmesh,jwpeterson/libmesh,capitalaslash/libmesh,capitalaslash/libmesh,dschwen/libmesh,dschwen/libmesh,BalticPinguin/libmesh,BalticPinguin/libmesh,capitalaslash/libmesh,jwpeterson/libmesh,roystgnr/libmesh,dschwen/libmesh,libMesh/libmesh,capitalaslash/libmesh,capitalaslash/libmesh,jwpeterson/libmesh,roystgnr/libmesh,jwpeterson/libmesh,BalticPinguin/libmesh,libMesh/libmesh,roystgnr/libmesh,libMesh/libmesh,capitalaslash/libmesh,dschwen/libmesh,libMesh/libmesh,capitalaslash/libmesh,BalticPinguin/libmesh,jwpeterson/libmesh,libMesh/libmesh,roystgnr/libmesh,libMesh/libmesh,roystgnr/libmesh,dschwen/libmesh