The tune comes from a Sephardic Jewish song called "Los Bilbilicos" (The Nightingales). As far as we've been able to determine, Richard Fariña was aware of the tune, but had no understanding of the meaning of the Ladino words of "Los Bibilicos." You may be interested in this thread (click) for background information on the song. I believe the tune is also used for a table grace in Hebrew.
-Joe Offer-