Fixed two horizontal indexing bugs in get_field_nc, where the difference
between the array starting index (always 1 in this subroutine) and the values
in the handle argument were not being taken into account when the array was
being passed in with only its computational domain.  Also initialized the
internal unlim_index array in get_netcdf_fields to fix a problem with using an
uninitialized array that was being flagged when run in debug mode.  With this
commit, the model is once again reproducing the expected answers when rescaling
is applied for vertical distances or time.  All answers are bitwise identical
in cases that were working before.

  This commit addresses the issue at github.com/NOAA-GFDL/issues/333, which
can be closed once this commit is merged into dev/gfdl.

This patch addresses some of the proposed changes to `get_field_nc`.

* `WARNING` is removed from `use MOM_error_handler` since it is unused.

* Zero initialization of `values_c` by `source=` has been removed.

  This initialization serves no purpose, since every value will be
  filled by the netCDF read statement.

* `values_c` indexing is now 1-based

  `values` has ambiguous shape, so it can follow no natural indexing.
  Although `values_c` always resides on the compute domain, the transfer
  to `values` may feel unintuitive.  Allocating from the 1 index
  identifies this as an explicit transfer of 1-based indices.

* Computation of the data domain indices were moved to the actual
  transfer of `values_c` to `values`.

* A comment was added to explain the initial "magic value" of
  `unlim_index`.

(It has also been suggested that the zero initialization of the intent(out)
`values` array should be removed, even when it has halos that would not be set
here.  However, this was deemed beyond the scope of this bug-fix PR, so this
commit was edited during merging to restore the initialization of `values` to
exactly what was there on the dev/gfdl branch before this PR, leaving this
particular change to be addressed with a later PR as necessary. - R. Hallberg)

Stylistic changes consistent with the existing file have also been
imposed:

* `values_nc` renamed to `values_c`

  Previous suffix indicated some special netCDF property of this field,
  when it's just the compute subdomain of the field's values.

* Comments have been truncated for readability

* Column width is restricted to 80

* Composite statements (semicolons) have been removed

  Made the values argument to MOM_read_data_2d and get_field_nc intent inout to
preserve the previous values of this array in any halos it might have, and
removed a line initializing the halos of this array to 0.  Also added some
missing comments describing arguments to these routines  and changed the
existing comments describing the arguments to get_field_nc to use doxygen
syntax.  All answers in test cases are bitwise identical.