including the merge of `hdffv/hdf5/develop`, back to the branch that Vailin and
I share.
Now I need to put this branch on a fork with a less confusing name than
vchoi_fork!
Check for smaller or larger section size after merging and shrinking a section,
for this case is the section that is smaller than threshold (see H5MF_xfree() in H5MF.c).
It is possible for the section to be smaller after merging/shrinking (see H5MF__sect_large_shrink()
in H5MFsection.c).
Given that the VFD SWMR configuration FAPL property is set, the writer field must
be consistent with the flags passed in the H5Fopen() (either H5F_ACC_RDWR for the
VFD SWMR writer, or H5F_ACC_RDONLY for the VFD SWMR readers).
