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/h5format_convert/testfiles/h5fc_d_file-d.ddl

@@ -0,0 +1,25 @@
+usage: h5format_convert [OPTIONS] file_name
+  OPTIONS
+   -h, --help                Print a usage message and exit
+   -V, --version             Print version number and exit
+   -v, --verbose             Turn on verbose mode
+   -d dname, --dname=dataset_name    Pathname for the dataset
+   -n, --noop                Perform all the steps except the actual conversion
+
+Examples of use:
+
+h5format_convert -d /group/dataset file_name
+  Convert the dataset </group/dataset> in the HDF5 file <file_name>:
+    a. chunked dataset: convert the chunk indexing type to version 1 B-tree
+    b. compact/contiguous dataset: downgrade the layout version to 3
+    c. virtual dataset: no action
+
+h5format_convert file_name
+  Convert all datasets in the HDF5 file <file_name>:
+    a. chunked dataset: convert the chunk indexing type to version 1 B-tree
+    b. compact/contiguous dataset: downgrade the layout version to 3
+    c. virtual dataset: no action
+
+h5format_convert -n -d /group/dataset file_name
+  Go through all the steps except the actual conversion when 
+  converting the dataset </group/dataset> in the HDF5 file <file_name>.