The longtime private-equity giant KKR finally has taken itself public. The problems of the real estate sector have handed the firm a few setbacks, and now it looks to a retail chain to give it a big win as a public company. The company is getting ready to take Dollar General Corp. public. The retailer's discount strategy has been a surprise winner through the recession. The real estate downturn wiped out KKR's investment in Capmark, previously the commercial real estate unit of GMAC.