It wasn’t exactly “Hi-yo Silver” for Walt Disney Co. shares; they suffered the Dow’s steepest fall. Disney, the world’s biggest entertainment company, said third-quarter profit was little changed from the same time last year amid costs to market the box-office disappointment “The Lone Ranger” and shrinking revenue at its ABC television network. Net income rose to $1.85 billion from $1.83 billion. The cool reaction to ‘‘The Lone Ranger’’ could lead to a fourth-quarter loss. Still, the stock is up 35 percent this year.