TOKYO (Reuters) - Asian stocks and the pound gained on Tuesday as investors held out hope that Britain still had a chance of avoiding a messy exit from the European Union at key negotiations this week.MSCI's broadest index of Asia-Pacific shares outside Japan was up 0.1%. Australian shares were up 0.17%, while Japan's Nikkei stock index was up 1.86%.The pan-region Euro Stoxx 50 futures rose 0.23%, German DAX futures were 0.16% higher, while FTSE futures were up 0.12%.The pound rose against..