Commission Regulation (EC) No 1054/98 of 20 May 1998 amending Regulation (EC) No 1223/94 laying down special detailed rules for the application of the system of advance-fixing certificates for certain agricultural products exported in the form of goods not covered by Annex II to the Treaty, and Regulation (EC) No 1222/94 laying down common detailed rules for the application of the system of granting export refunds on certain agricultural products exported in the form of goods not covered by Annex II to the Treaty, and the criteria for fixing the amount of such refunds