hdf5_ep

[svn-r27284] Modify VDS implementation to always use FAPL and DAPL from VDS file and dataset
to open source files and datasets, instead of using the default property lists.
Modify VDS to reject attempts at parallel I/O, fix parallel compile error.
Modify VDS to not write fill value to memory buffer if the fill value is
undefined.
Other minor fixes/cleanup.

Tested: ummon