Overriding getIndirect() to avoid parm caching errors.

This cryptic virtual function is used (internally by Houdini) to cache parameter indices, so that parm lookup by name is done only once. This seems to only affect the SceneCache OBJs because they're the only nodes which add their own parameters before base class parameters.

This solves the bug mentioned in the previous commit. All tests pass again.
Adding standard mantra geometry parms to SceneCacheGeometry OBJ.