De-duplicate the lists returned by iniGet/ReadSectionList()
I noticed a duplicate area name (AGN_MODS) in a filefix %LIST response from my FidoNet hub that's running TickIt/TickFix, and I thought to myself: Self, that shouldn't be possible. But alas, if one does have duplicate sections in a .ini file (e.g. tickit.ini), the iniGet/ReadSectionList() function would indeed return duplicate items in the list. Since the second section with the same name is not actually accessible, it shouldn't be counted as a valid section and thus not returned as part of the section list. Section names are not case sensitive, so the names are compared case-insensitively for de-duplication purposes too.