A seemingly major event for credit markets has historically sparked a sizable directional move in equities.There's never a dull moment on Wall Street. Earlier this year, the bulls could do no wrong, with the benchmark S&P 500 (^GSPC -0.67%) climbing to an all-time record high. Not long thereafter, a historic bout of volatility arrived.In April, the steady-footed S&P 500 endured its fifth-worst two-day percentage decline of the last 75 years. But true to form, less than a week after this mini-crash, the icon ...