The President, Major General Muhammadu Buhari (retd.), has told presidential aspirants in the ruling All Progressives Congress to go to the field and sell their candidatures to the electorate, Saturday PUNCH has learnt.   A Presidency source told one of our correspondents that Buhari did not ask any of those who consulted him to either run or drop their ambitions.   Rather, the President was quoted to have advised them not to compromise the integrity of the APC and the Federal Government in their campaigns.   So far, no fewer than eight aspirants in the ruling party have declared their