stdio module doesn't set "slowest" counters for non-shared files

The STDIO_SLOWEST_RANK_BYTES, STDIO_SLOWEST_RANK, and STDIO_F_SLOWEST_RANK_TIME (and possibly other) counters are set to zero in the output if the file is not opened by all ranks. It would probably be more helpful if they were set to the corresponding values for the rank in question so that you can more quickly compare these values across files whether they were shared or not.

Need to confirm this behavior in other modules too.