By Dan Weil The S&P; 500 has slid 13% so far this year, and the Bloomberg U.S. Aggregate bond index has lost 10%. From 2009 until early this year, stocks and bonds largely rose together. But now they’re falling together. The S&P 500 has slid 13% so far this year, and the Bloomberg U.S. Aggregate bond index has lost 10%. The indexes are on pace for their biggest simultaneous fall since 1976, when Dow Jones Market Data started following the numbers, The Wall Street Journal reports. The only other year when the two indices both fell was 1994, and that was only 1.5% for the S&P 500 and 2.9% for th…