Fixes trac:2028. George and I found this via some collaborative debugging

(yay cisco webex!).  Make sure we only go up to OPAL max datatype, not
OMPI max datatype.

This commit was SVN r22016.

The following Trac tickets were found above:
  Ticket 2028 --> https://svn.open-mpi.org/trac/ompi/ticket/2028

ompi/mpi/c/get_elements.c

@@ -86,8 +86,9 @@ int MPI_Get_elements(MPI_Status *status, MPI_Datatype datatype, int *count)
       }
       if( (*count) != 0 ) {
          int total;  /* count the basic elements in the datatype */
-         for( i = 4, total = 0; i < OMPI_DATATYPE_MAX_PREDEFINED; i++ )
+         for( i = 4, total = 0; i < OPAL_DATATYPE_MAX_PREDEFINED; i++ ) {
             total += datatype->super.btypes[i];
+         }
          *count = total * (*count);
       }
       if( size > 0 ) {