Comment 0 for bug 1237860

The greeter selector writes the user's gsettings key in the current version, we need to fix that.
(you need to export USS_SHOW_ALL_UI=1 since that control is hidden in the UI)

The issue is that the transfert callback always call "background.pictureUri = imageUrl;", we need a parameter to tell us what image got clicked and use "backgroundPanel.backgroundFile = imageUrl;" in the greeter case.

* Way to test the backend on the device:

you can call 'gdbus call --system -d org.freedesktop.Accounts -o /org/freedesktop/Accounts/User32011 -m org.freedesktop.Accounts.User.SetBackgroundFile '/home/phablet/Pictures/example.jpg"', where "32011" is the uid of the phablet user and the example.jpg and existing file

(it seems it needs to be in the user directory for some reason, I tried an /usr version and that didn't work)