[table] correct the minimum size of dimensions with spanned children
[table] correct the minimum size of dimensions with spanned children

The layout now uses the same algorithm as that used when the table is
set between minimum and preferred size. This prevents the layout from
jumping as it hits minimum size.

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