Fix distributed reads of checksums using FMS2_io

  Corrects reads of hexadecimal checksum attributes from distributed files when
using the FMS2 IO interfaces.  All answers are bitwise identical, and reads and
writes of distributed sets of restart files are now working with the FMS2 IO
interfaces.

config_src/infra/FMS2/MOM_io_infra.F90

@@ -484,6 +484,7 @@ subroutine get_file_fields(IO_handle, fields)
   character(len=256),  dimension(size(fields)) :: var_names ! The names of all variables
   character(len=256)  :: units    ! The units of a variable as recorded in the file
   character(len=2048) :: longname ! The long-name of a variable as recorded in the file
+  character(len=64)   :: checksum_char ! The hexadecimal checksum read from the file
   integer(kind=int64), dimension(3) :: checksum_file ! The checksums for a variable in the file
   integer :: nvar  ! The number of variables in the file
   integer :: i
@@ -503,8 +504,9 @@ subroutine get_file_fields(IO_handle, fields)
 
       fields(i)%valid_chksum = variable_att_exists(IO_handle%fileobj, var_names(i), "checksum")
       if (fields(i)%valid_chksum) then
-        call get_variable_attribute(IO_handle%fileobj, var_names(i), 'checksum', checksum_file)
-        fields(i)%chksum_read = checksum_file(1)
+        call get_variable_attribute(IO_handle%fileobj, var_names(i), 'checksum', checksum_char)
+        ! If there are problems, there might need to be code added to handle commas.
+        read (checksum_char(1:16), '(Z16)') fields(i)%chksum_read
       endif
     enddo
   else