Scale texture bitmaps that are not large enough

Scale texture bitmaps that are not large enough

Texture bitmaps are now sized up by an integer factor to be at least
as large as the board (if they seem intended for a full XQ board, which is
assumed when they are larger than 256x256) or the square. This necessitated
the textures to be re-initialized in InitDrawingSizes whenever the window
size changes.