MEXICO CITY (Reuters) - Mexico's biggest retailer, Wal-Mart de Mexico , said on Tuesday that sales at Mexican stores open at least a year fell 1.9 percent in February. The Mexican affiliate of Wal-Mart Stores Inc said February same-store sales in Central America also fell 1.9 percent from a year earlier. Walmex said total sales, including those from newly opened stores, rose 2.1 percent in February from a year earlier. The company opened eight new stores and restaurants in Mexico and Central America in February. Walmex last month told investors that it expects to spend up to $1. ...