widget: don't use the allocation as the paint volume for scrollable widgets
widget: don't use the allocation as the paint volume for scrollable widgets

The allocation for scrollable widgets cannot be used as the paint volume
because it does not account for any transformations applied during
scrolling.

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