I've run a clean install from latest cvshead on pg 8.3, then I run the check indexes script in xmldb and the following aren't created:

CREATE INDEX mdl_log_tim2_ix ON mdl_log (time);
CREATE INDEX mdl_chatmess_timcha2_ix ON mdl_chat_messages (timestamp, chatid);
CREATE INDEX mdl_chatmesscurr_timcha2_ix ON mdl_chat_messages_current (timestamp, chatid);