The checks for the headers at the start of HDF4 & HDF5 files have been
put in a static isHDF member to encapsulate the details about
checking for a HDF file and make it reusable.
It will not retain an open file handle to the file so does not
inherit from the standard FileDescriptor.
Refs #7263

and also defines two types of loader, NonHDF and HDF.
Refs #7263

Refs #7263

It was previously not updating the version map when the algorithm was
removed and then subscribing the same thing again would throw an error.
Refs #7263

The stream is open for as long as the object is alive.
Refs #7263

FileDescriptor uses streams rather than c file handles. Refs #7263

Currently based on string names.

Specifically, one of the ouput properies was not being set.
Unit tests checks of the output properties have been added.
The failure of the example was due to a change made by Pete in a previous ticket, but I've update the help text.

It was always logging (to debug) that it wasn't doing anything. No
it is a bit louder about it.

...in the peaks table of slice viewer.