One of Harrison Ford's most endearing qualities as a movie star is his easygoing, improvisatory genius. Everyone who's worked with him praises his instincts to fix a scene that's missing a certain, ineffable something. Occasionally, these adjustments arise out of necessity (e.g. the debilitating fever that turned a prolonged fight with a swordsman in "Raiders of the Lost Ark" into a one-and-done gunshot), but generally, he's just always thinking about how to make a good scene great, or a...