Set alpha depending on progress at completion time
Set alpha depending on progress at completion time

Otherwise, there's a race condition where alpha will be set to 0, 1,
and then 0 again if setProgress:animated: is called in quick enough
succession (basically, within the animation duration).
boherna/MRProgress,yungfan/MRProgress,mrackwitz/MRProgress,hanangellove/MRProgress,jackywpy/MRProgress,odyth/MRProgress,AddAloner/MRProgress,odyth/MRProgress,zaubara/MRProgress,colemancda/MRProgress,mrackwitz/MRProgress,AlexanderMazaletskiy/MRProgress,AlexanderMazaletskiy/MRProgress,yarry/MRProgress,zaubara/MRProgress,jackywpy/MRProgress,boherna/MRProgress,hanangellove/MRProgress,AddAloner/MRProgress,zaubara/MRProgress,yarry/MRProgress,colemancda/MRProgress,yungfan/MRProgress