Make LMM tests pass.

Also:
- Change LMM names from 'MS' to 'LMM'
- Make step rejection work correctly for LMMs
- Allow use of grid norms in util.check_diff() by passing delta
Merge branch 'step_size_control' of github.com:hadjimy/pyclaw into step_size_control

* 'step_size_control' of github.com:hadjimy/pyclaw:
  Improve the way information from previous steps is updated.