More robust System::point_* with subdomain vars
More robust System::point_* with subdomain vars

If we have subdomain-restricted variables, and we ask to evaluate one
on a boundary between elements that support the variable and elements
that do not, obviously we never want to try evaluating on one of the
latter.

jwpeterson/libmesh,libMesh/libmesh,BalticPinguin/libmesh,dschwen/libmesh,pbauman/libmesh,BalticPinguin/libmesh,BalticPinguin/libmesh,hrittich/libmesh,capitalaslash/libmesh,pbauman/libmesh,dschwen/libmesh,90jrong/libmesh,pbauman/libmesh,jwpeterson/libmesh,jwpeterson/libmesh,libMesh/libmesh,dschwen/libmesh,hrittich/libmesh,roystgnr/libmesh,hrittich/libmesh,BalticPinguin/libmesh,capitalaslash/libmesh,dschwen/libmesh,roystgnr/libmesh,libMesh/libmesh,capitalaslash/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,roystgnr/libmesh,capitalaslash/libmesh,90jrong/libmesh,BalticPinguin/libmesh,dschwen/libmesh,libMesh/libmesh,90jrong/libmesh,jwpeterson/libmesh,capitalaslash/libmesh,roystgnr/libmesh,90jrong/libmesh,roystgnr/libmesh,libMesh/libmesh,hrittich/libmesh,pbauman/libmesh,hrittich/libmesh,libMesh/libmesh,BalticPinguin/libmesh,hrittich/libmesh,pbauman/libmesh,90jrong/libmesh,pbauman/libmesh,dschwen/libmesh,capitalaslash/libmesh,roystgnr/libmesh,BalticPinguin/libmesh,dschwen/libmesh,capitalaslash/libmesh,90jrong/libmesh,jwpeterson/libmesh,jwpeterson/libmesh,libMesh/libmesh,90jrong/libmesh,90jrong/libmesh,jwpeterson/libmesh,90jrong/libmesh,dschwen/libmesh,pbauman/libmesh,hrittich/libmesh,hrittich/libmesh,libMesh/libmesh,capitalaslash/libmesh,jwpeterson/libmesh,hrittich/libmesh,pbauman/libmesh,roystgnr/libmesh,pbauman/libmesh