dtbook-to-odt creates absolute links to path on server when images=linked

When the `images=LINKED` option is enabled the odt contains links to the images instead of the embed image. That is fine. The problem however is that the `xlink:href` points to a temporary path on the server

``` xml

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If I modify these links to a relative path and place the images in the same directory as the odt file, the file opens correctly and the images are showing.

``` xml

```

Start at the dtbook-to-odt conversion entry point and reproduce the issue with images=LINKED. Inspect how the generated draw:image xlink:href is built, comparing the absolute temporary path with the expected relative path. Done means the ODT keeps linked images and opens them correctly when the images are placed beside it.

Written by the indexing model from the issue text.