Blender Git Loki

Fix T39897: shape keys created while the Relative checkbox is unchecked start out with frame=0

So! First, frame for absolute shape keys: never allow a new key to have the same pos as an
existing one (this does not make sense). This way, the two workflows are possible (create
all keys and then animate ctime, or animate ctime and then create keys where you need them).

Also, fixed UIList for shapekeys, the "absolute" test was wrong, and better to show frame
value, even though not editable, than nothing in case of absolute keys.

And finally, add getter to RNA 'frame' readonly value, so that we output real frame values,
and not dummy internal ones (which are /100) in our API.