Tool icon's requested size is 24x24, but our legacy icons provide 22x22.
This makes them superseded by our new default icon theme.
The trick is to pretend in the Legacy theme description (index.theme)
that the 22x22 tool icons' nominal size is 24x24.
It will makes nostalgic people happy. It does not change the plans about
the new Color icon theme, which we are planning to render pixel-perfect
as well in the end.
