The bug document has:
<style:page-layout-properties ... style:repeat="no-repeat">
<style:background-image ... style:repeat="stretch"/>
</style:page-layout-properties>
When a stretched background image is set on a page style using the Writer UI,
then these two style:repeat attributes always match, but not in the bugdoc.
The later used to have priority, till commit
7d9bb549d498d6beed2c4050c402d09643febdfa (Related: #i124638# Second step of
DrawingLayer FillAttributes..., 2014-06-02).
Fix the problem by extending XMLBackgroundImageContext::EndElement(): if we
know that the <style:page-layout-properties> sets the FillBitmapMode property,
then don't blindly set BackGraphicLocation, but try to overwrite the exiting
FillBitmapMode one.
Change-Id: I64ab4363b20cc95003d35acd63ea421472b1c071
6621da38b3