Apple has offered to replace faulty on-off buttons on the iPhone 5, a rare glitch which it admitted affected “a small percentage” of the previous-generation smartphones. Apple said on its user-support page that “iPhone 5 models manufactured through March 2013 may be affected by this issue,” in which the button, also known as a sleep/wake mechanism, stops functioning or works only intermittently.  It did not say how many phones were shipped with the faulty mechanism. Owners can type in their...