I would like to make relative links to pictures in an Inkscape file. So when I move the project files (images and the Inkscape master), I wouldn't have to relink the images.
What is the proper way to do this?
After saving, closing, and moving your svg file along with your image file, Inkscape should still display the image in your file. Also note that after re-opening, Inkscape will keep the xlink:href attribute, but also maintain a separate attribute called sodipodi:absref that will store the absolute location of the image. I've found that this doesn't matter -- you can still move your files around and Inkscape will refer to the xlink:href attribute to find your image.
Tested on Inkscape 0.48
../stuff/file.ext indeed should work.
For a full guide see here: http://libregraphicsworld.org/blog/entry/inkscape-embedding-or-linking ;-)