*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 and split it into
     the two routines smooth_x9_h and smooth_x9_uv to reduce the memory used by
     this routine and reduce the use of optional arguments.

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

  4. Added new integers to indicate the loop ranges over which the viscosities
     and related variables should be calculated, depending on which options are
     active, and then adjusted 91 do-loop extents horizontal_viscosity code to
     reflect the loop ranges over which arrays are actually used.

  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.

  These revisions change answers when USE_LEITHY is true, but answers are
bitwise identical in all other cases.