Comment 8 for bug 170225

First patch attached.

Tested on Windows XP and Ubuntu 10.10, revision 10074.
On Windows, relative hrefs are saved as pathnames with / as path separator (instead of \) so that they can be opened on other operating systems. Thus they can be considered as relative IRIs and thus conform to the W3C recommendations (I'll dig a bit later to be absolutely sure of it).

Known bug: an image imported in an unsaved new document needs to be saved twice before being saved as relative.

There's some work left, but you can already test and comment!