Fix interleaving offsets and stride not getting inherited

Nodes inheriting VBOs from other nodes need to get the correct
interleaving parameters from them as well to render the geometry
correctly. Fixes regression from commit "Interleave vertex attributes
into a single buffer for more efficient drawing". Tested by
examples/geometry/vertexSharing.html.
Merge pull request #315 from NVIDIA/fix-vertex-sharing

Fix interleaving offsets and stride not getting inherited