fix crash in getExternalValues if source and data views are model-based and have different elements available (reported by laurent)

the size is correct (so that they can be used on proxies)

complex numbers

Several things for multi-constraint mesh partitioning + start circumscribed circle of MElement (need to be finished)

structure (not sure what was wrong though)

Camera mode is avaiable with camera aperture tuning
stereo is available on stereo device only, otherwise the program
makes a segmentation fault with a openGL message :

"Insufficient GL support
 new gl windows for stereovision0x9477658
 Erreur de segmentation"