hdf5

[svn-r27479] Add checking for invalid inputs to H5Dset_virtual: point selections, incorrect
numbers of elements selected, incorrect "slice" through limited dimensions,
incorrect number of printf substitutions.
Patch source selection space extent with bounds of selection if extent is
unknown before returning via H5Pget_virtual_srcspace.
Write updated VDS dataspace to file when it changes due to unlimited selections.
Other minor fixes/cleanup.

Tested: ummon