Modifications have been made to correct behavior of h-adaptivity with hi...

...gher order SZABAB and BERNSTEIN:

--  defined SZABAB to be hierarchic

-- defined compute_constraints function for SZABAB and BERNSTEIN

-- defined extra_hanging_dofs for SZABAB and BERNSTEIN to be true

-- FEInterface::compute_constraints for SZABAB and BERNSTEIN now call the compute constraint functions for the respective elements.