OK, now that I understand how easy it is to do per-row stuff in db_multirow (completely explained in the api documentation if I'd only looked at it), I've now posted what I think is a correct and useful cvs patch for Forums. This inserts calls to ad_quotehtml at appropriate places in tcl and makes no skanky alterations of adp.
The patch is here: http://sdm.openacs.org/sdm/one-patch.tcl?patch_id=512