symetric mates

[bastien.dissaux]

References 1 and 2 should be able to come from the same piece if necessary without create plan ! 

And we must have the possibility to constraint 2 faces between 2 other without create another plan in my part.

On the video : 

If i select first blue and red faces, and yellow and green in second, the yellow/green should be in the middle of red/blue