Two old musicals lack new life by Ed Siegel
WILLIAMSTOWN -- How important is it to bring something new to the table when you're mounting a classic musical? If the source material is strong, why not leave well enough alone and let the music and story speak for themselves?<br /> That's what two directors in the Berkshires have done with very different musicals, ''The Threepenny Opera'' and ''Funny Girl.'' While both are well mounted and beautifully sung, the res…