o multi-threading and IO:   - all threads call READ_FLD S/R (needed if using SingleCpuIO):     (no BEGIN_MASTER/ END_MASTER around the call, but inside MDSIO S/R.   - barrier before and after reading.   - stop if other than master is calling MDS_WRITELOCAL (if #undef IO_THREAD_SAFE)   - avoid using MDS_WRITELOCAL for LAND pkg output.   - new S/R AIM_WRITE_PHYS (replaces AIM_WRITE_LOCAL) to write AIM physics     common-block variables ; Allows multi-threading with master-thread IO.
o multi-threading and IO:
  - all threads call READ_FLD S/R (needed if using SingleCpuIO):
    (no BEGIN_MASTER/ END_MASTER around the call, but inside MDSIO S/R.
  - barrier before and after reading.
  - stop if other than master is calling MDS_WRITELOCAL (if #undef IO_THREAD_SAFE)
  - avoid using MDS_WRITELOCAL for LAND pkg output.
  - new S/R AIM_WRITE_PHYS (replaces AIM_WRITE_LOCAL) to write AIM physics
    common-block variables ; Allows multi-threading with master-thread IO.

altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h,altMITgcm/MITgcm66h