This PR fixes a crash caused by the improperly ensured lifetime of RigGeometry::mSourceGeometry. mSourceGeometry was not adequate to ensure mSourceGeometry would outlive mGeometry because we extend mGeometrys lifetime beyond this lifetime by passing mGeometry to the draw traversal instead of this.
In addition,
We add important comments.
We detect and prevent generally unsafe operations in high level code.
We add a sprinkling of const to help clarify intentions.
This PR proposes a simple change to `RigGeometry` `dirtyGLObjects` logic.
1. We will avoid dirtying unmodified arrays.
2. We can drop an osg version guard since `Drawable::dirtyGLObjects` is not nearly as harmful as `Geometry::dirtyGLObjects`.
3. We will avoid crashes in an as yet unfinished future PR concerning `Array` sharing improvements.
Double buffering, custom bounding box and the update in the cull visitor (instead of update) are now all handled internally rather than needing hacks and/or callbacks.
