UPDATE 3-UnitedHealth boosts dividend by 30 percent

3:32pm BST * Sets new stock buyback program * Follows strong Q1 by UnitedHealth, rivals * Shares down 0.3 percent (Adds analyst comment, share movement, byline) By Lewis Krauskopf NEW YORK, May 25 (Reuters) - UnitedHealth Group Inc (UNH.N: Quote,...