Add DiffContext::n_dof_indices()
Add DiffContext::n_dof_indices()

This lets us downcast from STL size() in one place

Also it's probably better for encapsulation or something.

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