ANJAR, Lebanon, Dec 4 (Reuters) - Lebanese forces excavated a suspected third mass grave on Sunday, a day after unearthing 25 decomposed corpses in an eastern town that was the headquarters of Syrian intelligence for three decades. Security forces were digging for more bodies at the third site near two other mass graves close to an old onion farm in the eastern town of Anjar, long used by Syrian intelligence as a notorious interrogation centre. Security sources said the 25 bodies found so far -- most now only skeletons in scraps of underwear -- had lain in the shallow graves...