Remove iterator boilerplate from SystemSubsetBySubdomain.
Remove iterator boilerplate from SystemSubsetBySubdomain.

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