Fix for bug #688 (documentation building)

[Vincent Béron]

This one I'm not sure which one is better. So I include both patches,
but only one should be applied.

Functionnally, both produce the exact same html files, although the fix1
creates (by the system's db2html) a directory with images (which are
unused).

So I'd tend to go with fix2.

Please comment, and I'll post the good one to wine-patches.

Vincent