[Dev-luatex] Proposal for a change in otfl-luat-dum.lua

To be able to use fonts inside a dfont archive (Helvetica for example) I had to change line 59 in otfl-luat-dum.lua to " dfont = "truetype fonts",". When I updated my mactex 2010 installation a few days ago, the file got overwritten and I had to do the change again. I'm not sure if there is a better/cleaner solution but since this small change works for me, this could at least be used as a temporary fix.