[camera] Fix camera handling for blender version < 2.65

The groupMembers api has changed of name several times so deal with it.
Moreover, this API has been added only in 2.63 so 'deal' with it. In
this case, there is no proper way to handle 'grouped object' so #509
will still be an issue.
[core] Remove test against blender < 2.62

We only support Blender 2.62+, so remove test against previous version.
It should be particularly useful here, as transformation3D is probably
an 'hot path'.