Commission Regulation (EC) No 1144/1999 of 31 May 1999 amending Regulations (EC) No 1758/98, (EC) No 1666/98, (EC) No 1667/98, (EC) No 1735/98, (EC) No 1759/98, (EC) No 1760/98, (EC) No 2198/98, (EC) No 1123/98, (EC) No 1641/98, (EC) No 1066/1999 and (EC) No 1067/1999 opening standing invitations to tender for the export of cereals held by certain intervention agencies