Slideshow has no transition(s?)

[AlbatorV]

@Jon

The internal viewer's slideshow can now use a crossfade transition between images. Activate it using the Show SLIDESHOW=fade argument. The Show VIEWERCMD=slideshow command can also specify fading, e.g. Show VIEWERCMD=slideshow:fade,on

No slideshow effect for me with this new command.
Slideshow does not start.