Dollar General fired a salvo against Family Dollar CEO Howard Levine in a formal letter to Family Dollar's board, saying that Levine appears to be acting in his own self-interest, not his company's, in merger negotiations with Dollar General and Dollar Tree, according to a report by the Wall Street Journal. Family Dollar (NYSE: FDO) is in the middle of an apparent bidding war between its rival discount retailers, Dollar Tree (NASDAQ: DLTR) and Dollar General (NYSE: DG), but ever since Dollar General…