Bug#826522: Set the plugin directory

[Jérôme Kieffer]

Dear HDF5 package maintainers,

Currently the debian build system does not enforce the plugin directory
for HDF5 filters, defaulting to "/usr/local/hdf5/lib/plugin". I guess
Debian would prefer something like:
"/usr/share/hdf5/plugin" or even better:
"/usr/lib/x86_64-linux-gnu/hdf5/plugins".

Would it be possible to specify the option --with-default-plugindir=/usr/lib/x86_64-linux-gnu/hdf5/plugins
to ./configure in order to re-locate those plugins and offer in
external packages those plugins.

At synchrotrons, some of our detectors use LZ4 compression in HDF5
files. Having plugins packaged and directly installable is real
advantage compared to other operating systems.

Thanks for you comprehention.
With my best regards,

Jérôme Kieffer

REF: https://github.com/silx-kit/silx/issues/113