Hi Liliana and all.  Until now the user could decide what image loaders
to install alongside.  Or so I thought.  However, surprisingly I cannot
get any other loader except gdk-pixbuf and librsvg to work anyway.

That is,

guix shell viewnior webp-pixbuf-loader

surprisingly does not see webp files.  I do not understand.

If this changed patch looks fine, now with proper gexp use, I will push
it.  The patch continues to include gdk-pixbuf among the inputs even
though gtk+@2 propagates gdk-pixbuf anyway, but better be explicit.

Regards,
Florian