+Add optional unscale argument to check_redundant

  Added an optional unscale argument to the various check_redundant routines so
that the values that are written out in error messages are independent of
rescaling values.  Also added or amended comments to document the units of
numerous internal variables and function arguments in MOM_debugging.F90.  All
answers are bitwise identical, but there are new optional arguments to several
publicly visible routines.