make.graphic.viewport — Use tables in HTML to make viewports for graphics
img element only supports the notion
of content-area scaling; it doesn't support the distinction between a
content-area and a viewport-area, so we have to make some compromises.
make.graphic.viewport is non-zero, a table
will be used to frame the image. This creates an effective viewport-area.
Tables and alignment don't work together, so this parameter is ignored if alignment is specified on an image.