BOCA RATON, June 3 (Reuters) - The private equity industry is going to be hit by volatility in accounting for their assets, as newly adopted rules force them to mark down the value of their portfolios, high profile private equity bosses cautioned on Tuesday. Mark-to-market, or “fair value” accounting, took full effect this year, requiring companies to value assets at current comparable prices. The rules are known as FAS 157, which defines how companies should use fair value, and FAS 159 which...