[NbtkBoxLayoutChild] pack the object struct more efficiently
[NbtkBoxLayoutChild] pack the object struct more efficiently

clutter-project/mx,jonnylamb/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,pwithnall/mx,clutter-project/mx