added brlcad._bindings.BRLCAD_VERSION; conditionally add HRT primitive;

Hi Bryan,

This patch is needed to work with BRL-CAD 7.24.0, where the Heart primitive is not yet existing.

The latest 7.24.1 from svn is currently broken, I will add patches to fix that.

On windows the installation of 7.24.0 works (with this patch), but test_wdb.py will seg-fault, I will need to debug it (probably some data type mismatch between architectures, will need to figure it out).

Cheers,
Csaba