keep.relative.image.uris xslt bug

I seem to have found a bug with the stylesheets and image paths when
generating html.  Prior to 1.66, image paths in the xml just passed
right through to html.  Upon upgrading to 1.68.1 I found that image
paths were calculated relative to the source directory you were in.  It
seems also that the parameter '$keep.relative.image.uris' should cause
the pre-1.66 behavior to return, however it doesn't.

Attached is a small testcase showing that no matter what, the image path
generated in the test.html file is 'concepts/images/lorem_ipsum.png'
where I expect it to be 'images/lorem_ipsum.png'.

This testcase is also available on the web:
iwana.kavi.com/~brett/docbookbug.tgz

-Brett