When deriving a state variable with ghost cells, the derive function in AmrLevel does a FillPatch for the individual state variable. However, in PeleC, the PCHypFillExtDir function can only operate on the full state, not individual variables. Therefore, instead of using the AmrLevel derive function in this case, we should manually FillPatch the whole state and then take the component that we need.

Resolves #706 (the only time this problem comes up right now is when using the adjacent_difference_greater refinement criterion with a state variable, which requires a ghost cell). Also cleans up the derive for LES variables, adds error checking to PCHypFillExtDir to ensure it is only called for the full state, and adds adjacent_difference_greater to a test case.