PetscViewerHDF5OpenGroup: Consider NULL group as /.

Employ PetscViewerHDF5Traverse_Internal.

PetscViewerHDF5ReadSizes_Private: SETERRQ global comm where appropriate

PetscViewerHDF5ReadSizes_Private: fix error message

PetscViewerHDF5Load: rearrange to throw the proper error

fix 'uninitialized' warning in hdf5v.c

inarg validation fixes

update use of attribute IO elsewhere in petsc

PetscViewerHDF5ReadAttribute: check attribute existence

PetscViewerHDF5{Has,Write,Read}ObjectAttribute impl.

PetscViewerHDF5{Read,Write}Attribute: Allow for the current group.

Use PetscViewerHDF5GetAbsolutePath_Internal().

PetscViewerHDF5HasAttribute: Allow for the current group.

Use PetscViewerHDF5GetAbsolutePath_Internal().

PetscViewerHDF5GetAbsolutePath_Internal impl. and used in PetscViewerHDF5HasObject

PetscViewerHDF5HasObject rewritten to allow for the current group

PetscViewerHDF5Traverse_Inner_Internal factored out

PetscViewerHDF5HasGroup impl.

inarg validation fixes

rename PetscViewerHDF5HasObject_Internal -> PetscViewerHDF5Traverse_Internal

PetscViewerHDF5WriteAttribute: create group if it doesn't exist

PetscViewerHDF5HasAttribute_Internal factored out (doesn't test parent)

PetscViewerHDF5HasAttribute: make use of HDF5 1.8.0+ API

PetscViewerHDF5HasAttribute: support group attributes

PetscViewerHDF5HasAttribute: fail if parent is not dataset

PetscViewerHDF5HasObject_Internal can create the group hierarchy

PetscViewerHDF5HasObject_Internal: output args made optional

PetscViewerHDF5HasObject_Internal more robust - test every group in hierarchy