Doxygen was confused by the unsupported modules being partly in the doc/
directly, instead of completely in unsupported/doc/ . Thus, the link to
the unsupported modules on the server did not work (I think this manifested
itself after doxygen was upgraded on the server).
(transplanted from changeset 7898281b2b29fcb74fe9b78d9382e6ca91c25f5d
)