NEW YORK — After almost 10 years, Wall Street’s rally looks like it’s ending.Another day of big losses Friday left the U.S. market with its worst week in more than seven years. All of the major indexes have lost 16 to 26 percent from their highs this summer and fall. Barring huge gains during the upcoming holiday period, this will be the worst December for stocks since 1931.There hasn’t been one major shock that has sent stocks plunging. The U.S. economy has been growing since 2009, and most experts think it will keep expanding for now. But it’s likely to do so at a slower pace.