xdg-icon-resource
* Add pre-XDG Base Dir gnome-support
* Add "query theme"
* Add "query lookup"

xdg-email
* revisit decision to disable &attach= in mailto URLs

xdg-screensaver
* Return error when WindowID doesn't exist

General
* Support XDG_DATA_INSTALL
* Support XDG_INSTALL_HOOK
* Use "FILE" as argument everywhere instead of "file"
* Add xdg-autostart

xdg-su:
* It would be useful if it was possible to distinguish between a failure
because of a bad password or some other failure.
* use sudo style syntax, drop -c option