By , , LONDON/SAN FRANCISCO/TOKYO (Reuters) - U.S. equity futures fell and volatility indicators turned jumpy as a chaotic presidential debate between incumbent Donald Trump and Democratic challenger Joe Biden heightened fears that a disputed ballot could lead to a messy transfer of power.Nagging doubts over whether Republican President Trump would agree to hand over the keys to the White House if he loses have grown in recent weeks. And during the first debate on Tuesday, Trump declined to commit to accepting the results, repeating his unfounded complaint that mail-in ballots would lead to...…By , , LONDON/SAN FRANCISCO/TOKYO (Reuters) - U.S. equity futures fell and volatility indicators turned jumpy as a chaotic presidential debate between incumbent Donald Trump and Democratic challenger Joe Biden heightened fears that a disputed ballot could lead to a messy transfer of power.Nagging doubts over whether Republican President Trump would agree to hand over the keys to the White House if he loses have grown in recent weeks. And during the first debate on Tuesday, Trump declined to commit to accepting the results, repeating his unfounded complaint that mail-in ballots would lead to...WW…