Preparing for cortex installation.

Setting version a14 in Sconstruct and updating Changes file.
Fixing compatibility issues for Houdini 12.1 introduced by GEO_CortexPrimitives
Bug fix on instances showing superimposed with the original GL group.

Making sure the GLGroups pointed by the instance map contain the transform matrix.
Merge branch 'master' of https://github.com/ImageEngine/cortex