Check for a following argument to --implicit_neighbor_dofs in
DofMap::use_coupled_neighbor_dofs().  This allows the user to
explicitly disable the --implicit_neighbor_dofs option in cases where
he has all discontinuous variables, but doesn't want implicit neighbor
coupling.

I had to add LibMesh::command_line_next() to get this to work... for
some reason libMesh::command_line_value() was not working for me?