The package is (correctly) named 'accountsservice' (with two 's'), but the attribute and expression path lacked one 's'. Fix it.
This change has been successfully tested on gnome 3.12 (thanks @lethalman!). Now bring it to gnome 3.10, which currently is the default gnome3 version in NixOS. I've build and run tested it (success: smb:// protocol now work in Nautilus).
