Translated documents store their own parent links

Links to the parent pages are stored separately for each translations of a documents.
This is not a good design, since a translation should have the same parent as the original document. This is partially enforce by the way xwiki looks for parents in most places, and the issue stay clearly hidden in most places but this has sometime very weird effect:

• parent link shown in the editor for translation is not correct
• during renaming, backlinks shown differ if you start from a translations and it has a different parent then the original
• breadcrumb use the original document parents (which is good, but may be seen as unexpected)
• ... probably many other place I have not seen