Fel and Demon armor no longer has a duration, so changed code to this:

      {SMARTBUFF_FELARMOR, 0, SMARTBUFF_CONST_SELF, nil, nil, nil, S.LinkWarlockArmor},
      {SMARTBUFF_DEMONARMOR, 0, SMARTBUFF_CONST_SELF, nil, nil, nil, S.LinkWarlockArmor},

Also tried adding Soul Harvest with:

In apropriate lines in the buff.lua

  SMARTBUFF_SOULHARVEST     = GetSpellInfo(79268); --"Soul Harvest"

      {SMARTBUFF_SOULHARVEST, 0.5, SMARTBUFF_CONST_ITEM}

And in the main code:

      if (bUsable and sPlayerClass == "WARLOCK" and buffnS == SMARTBUFF_SOULHARVEST and UnitPower("player", 7) == 3) then
        bUsable = false;
      end

This does, however, not work. Not sure why. But it'd be nice having Soul Harvest as well to make it easier to regain chards inbetween battles.