He wasn't referring to restarting it. He means force closing an app. Holding down the power button until slide to power off shows up, then holding down the home button until I takes you to the home screen.
As far as I recall, it never closed all apps. I always thought it only closed the current app you were in. I could be wrong though. This method still works (just tried it) but you have to press the home "button" a lot longer than you used to.
Edit: it closes it, but does not quit the app. It's still in the app switcher when I double click (or 3D touch the left edge of screen.)
nevermind, this did something different from what I first thought
[doublepost=1475194711][/doublepost]it force closes the apps, but you still see the cards in the app switcher