refs #426 restore legacy behaviour and hdf4 and mxml functionality
refs #426 restore legacy behaviour and hdf4 and mxml functionality

this is not a proper fix, as it changes hdf5 behaviour based on
hdf4 or mxml option being enabled at runtime
The purpose was to narrow down the problem. Working legacy code is
a desired side outcome while implementing a better fix.

nexusformat/code,nexusformat/code,nexusformat/code,nexusformat/code,nexusformat/code