Fixes Glass objects position during dragging
Fixes Glass objects position during dragging

- while dragging, Glass object is rendered so that mouse is always in the
  middle of the object

dkoeb/f-spot,dkoeb/f-spot,mans0954/f-spot,mono/f-spot,dkoeb/f-spot,mono/f-spot,NguyenMatthieu/f-spot,mans0954/f-spot,dkoeb/f-spot,mans0954/f-spot,mans0954/f-spot,mono/f-spot,mono/f-spot,dkoeb/f-spot,mono/f-spot,dkoeb/f-spot,mans0954/f-spot,NguyenMatthieu/f-spot,NguyenMatthieu/f-spot,NguyenMatthieu/f-spot,mono/f-spot,mans0954/f-spot,NguyenMatthieu/f-spot