Changes to Commission Regulation (EEC) No 1643/76 of 7 July 1976 on the exceptional intervention measures in the beef and veal sector to be taken in certain regions of the Community most affected by the drought: Commission Regulation (EEC) No 1896/76 of 29 July 1976 extending the period of validity of the system of exceptional intervention measures in the beef and veal sector to be taken in certain regions of the Community most affected by the drought