Images missing in learning manual doc build

[Graham Percival]

John, sorry to add another thing to your plate, but could you 
investigate this?

When I do "make web" in Documentation/user/ the manual is great.  Images 
for all examples, everything working in Documentation/user/out-www/

When I then do "make web" in the topdir, the Learning Manual is missing 
the images in out-www/offline-root/.  The actual text is there, the HTML 
links are there, and the images are present in Program Usage and the 
User Manual, but not in the LM.  As far as I can tell, I've duplicated 
the build stuff for "lilypond-program" with "lilypond-learning", but 
evidently I missed something, and I can't figure it out.

Cheers,
- Graham