DSO Music Director Laureate Leonard Slatkin leads the ensemble this weekend in works by Hector Berlioz, Mohammed Fairouz and Modest Mussorgsky/Maurice Ravel. WRCJ’s Peter Whorf speaks with Maestro Slatkin at Detroit’s Orchestra Hall about Mussorgsky’s Pictures at an Exhibition…and DSO concerts later this season celebrating Slatkin’s 75th birthday…