Merge all of my changes from merge-back-to-feature-vfd_swmr-attempt-1,

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!

tools/test/misc/testfiles/h5clear_missing_file.ddl

@@ -20,4 +20,3 @@ h5clear --increment file_name
 
 h5clear --increment=512 file_name
   Set the EOA to the maximum of (EOA, EOF) + 512 for the file <file_name>.
-h5clear error: missing file name