[NbtkIconView] Sink the cell renderer reference when we're given it
[NbtkIconView] Sink the cell renderer reference when we're given it

When nbtk_icon_view_set_cell_renderer () is called with a renderer we should
sink the floating reference from the GInitiallyUnowned.

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