When the GL_EXT_pixel_transform extension is not present, we must use a special
routine in order to transform an OpenGL surface (e.g. a pbuffer) to another
OpenGL surface. We do this by copying from the source surface one tile at a
time into a cached texture, and then render a texture-mapped quad to the
screen (which will be transformed by the MODELVIEW matrix).

Unfortunately, this mechanism is currently broken, causing the resulting image
to look fractured and/or upside-down. The attached testcase demonstrates the
problem quite easily (Duke should not be upside down in the rotated image).