fallback rendering, we'll need to have swrast_texture_image objects.
* from this info, so just allocate this one level.
/* If this image disrespects BaseLevel, allocate from level zero.
* Usually BaseLevel == 0, so it's unlikely to happen.
* a miptree, so create one just for our level and store it in the image.
* It'll get moved into the object miptree at validate time.
* kernel.  Need to explicitly map and unmap it.
+ * sometimes fall back to using the swrast module for software rendering.
/* If intelImage->mt != NULL, image data is stored here.
* Else if intelImage->base.Data != NULL, image is stored there.