PDF import exploits viewBox Bug

This is a follow-up to Bug #166885 (https://bugs.launchpad.net/inkscape/+bug/166885)

On importing a PDF containing an embedded bitmap, you get something like this:
<g
  transform="matrix(2599.65,0,0,1949.74,141.732,141.732)"
  id="g2441">
  <image
    id="image2443"
    xlink:href="data:image/png;base64,..........." (shortened)
    transform="matrix(1,0,0,-1,0,1)"
    height="1"
    width="1" />
</g>

Appart from the strange upside/down flip, the important thing about this is: the image is initially scaled to a height and width of 1, and only subsequently stretched again to its original aspect ratio. This only works correctly assuming an attribute
preserveAspectRatio="none"

As Bug #166885 states correctly, this is not SVG-conformant (where preserveAspectRatio="xMinYMin meet" is stipulated as the default) and leads to other renderers displaying the image distorted. Additionally, fixing the above mentioned bug would lead to a faulty PDF import.