+(*)Correct rotational symmetry with USE_LEITHY

  This commit revises the smoothing code used when USE_LEITHY = True to give
answers that respect rotational symmetry and it also corrects some horizontal
indexing bugs and problems with the staggering in some halo update and smooth_x9
calls and reduces some loop ranges to their minimal required values.  The
specific changes include:

  1. Corrected a horizontal indexing bug when interpolating Kh_h and Ah_h to
     corner (q) points when USE_LEITHY = True.  These had previously been
     inappropriately copied from the thickness point to the southwest of the
     corner point.  This required symmetric-memory-mode calculations of the
     thickness point viscosities whenever USE_LEITHY is true, but to avoid adding
     complicated logic, the symmetric-memory loop bounds are used for the
     calculation of Kh.

  2. Revised smooth_x9 to give rotationally symmetric answers.  The previous
     code was retained behind the new nonsym_sums logical argument to smooth_x9
     to generate the previous non-rotationally symmetric answers if they are
     actively being used.  However, if they are not actively being used, all the
     unused code hidden behind the broken_symmetry=.true. branch in smooth_x9
     should be eliminated.

  3. Added the new runtime argument LEITHY_NONSYMMETRIC_SUMS in cases when
     USE_LEITHY = True to determine whether to use the new rotationally symmetric
     smoothing code.

  4. Eliminated 4 unneeded halo update calls, and added error handling for the
     case where Leith options are used with insufficiently wide halos.

  5. Added a new 2-d variable for the squared viscosity for smoothing that can
     be used for halo updates and to avoid having a variable with confusingly
     inconsistent dimensions at various points in the code.

  6. Corrected the position arguments on 2 smooth_x9 calls and 4 pass_var calls
     that are used when USE_LEITHY=.true. and SMOOTH_AH=.true.  As previously
     written, these smooth_x9 and pass_var calls would work when in non-symmetric
     memory mode but would give incorrect answers when in symmetric memory mode.

  7. Adjusted 13 do-loop extents in the USE_LEITHY=.true. code to reflect the
     loop ranges over which arrays are actually used, and another 78 loops now
     always work as though they are working with symmetric-memory.

  These revisions can change answers when USE_LEITHY is true, but answers are
bitwise identical in all other cases.  There are new or corrected entries in
some MOM_parameter_doc files.