MPI_File_get_info fails to return hints as required by MPI standard

[wkliao]

When calling MPI_File_get_info() right after MPI_File_open() with MPI_INFO_NULL, the returned info_used does not contain any the hints used by OpenMPI, as the number of keys in info_used is 0. (I am using 5.0.8 release).

According MPI 4.0 quoted below, info_used should contain all hints implemented in OpenMPI and their default values.

MPI_File_get_info returns a new info object containing the hints of the file 
associated with fh. The current setting of all hints related to this file is
returned in info used. An MPI implementation is required to return all hints
that are supported by the implementation and have default values specified;
...

MPI_File_get_info() needs to be fixed.