Hydrogenolysis of benzylidene acetals: synthesis of benzyl 2,3,6,2′,3′,4′-hexa-O-benzyl-β-cellobioside, -maltoside, and -lactoside, benzyl 2,3,4,2′,3′,4′-hexa-O-benzyl-β-allolactiside, and benzyl 2,3,6,2′,3′,6′-hexa-O-benzyl-β-lactoside