Houdini 12.5 Compatibility

I have disabled the GR_RenderHook for Houdini 12.5 or later. Newer versions of Houdini will use a GUI_PrimitiveHook to draw custom geometry in the viewport. I'll add that in a separate pull request. This one is just focused on building and passing the tests.

Note that one test has been temporarily disabled (for 12.5 builds only) due to a bug in OBJ_SubNet::getBoundingBox(). I've reported the issue to SideFx and will re-enable the test once they fix the problem.