Changes

I updated adj_low_res_nu for use with a generalized grid. It is
not called from within advance_clubb_core or from within SILHS.
It is not necessary to be generalized for tests within standalone
CLUBB. However, it is necessary to generalize this code for use
within host models, particularly for CAM and E3SM.

Since the call to adj_low_res_nu is not tested by CLUBB's main
ascending vs descending grid test (since it is not called from
within advance_clubb_core or from SILHS), I added it to the
reverse grid direction G Unit test so that the results from
ascending vs. descending grids get checked.