Fix error when fade=no for a popover.

Since we waited for the fade transition to end before destroying a popover,
popovers would never disappear if you turn fade off.

@hanakimis @bigsley @Dylnuge 
Yep, definitely needs to be done this way - otherwise you could even start with `fade: true` and then switch to `fade: false` and you'd get the same error we're trying to avoid!