A packet of envelopes <a href="http://al4a.fun#overturn" rel="nofollow">al4a</a>  TOKYO, July 26 (Reuters) - Tokyo shares tumbled on Friday onthe back of a stronger yen and the dollar languished at afive-week low against a basket of currencies as investors waitedfor clarity on U.S. stimulus at the Federal Reserve's policymeeting next week.