incorrect logic for setting XDG_DATA_DIRS

[Björn Lindqvist]

Please reassign to the right component if it should be something other than "debconf". The bug is in the file: /etc/X11/Xsession.d/60x11-common_xdg_path It was originally discovered in http://blog.sarine.nl/2012/03/04/gnome-3-and-setting-custom-xdg_data_dirs/ but I can reproduce it in ubuntu 15.10.

If you want to add extra XDG_DATA_DIRS, you ought to be able to write something like:

export XDG_DATA_DIRS="$XDG_DATA_DIRS:/opt/emacs/share"

But then the default xdg data dirs wont be added, causing lightdm to crash when you login. Essentially, the line:

XDG_DATA_DIRS=/usr/share/"$DESKTOP_SESSION":"$XDG_DATA_DIRS"

should be changed to:

XDG_DATA_DIRS=/usr/share/"$DESKTOP_SESSION":"$DEFAULT_XDG_DATA_DIRS":"$XDG_DATA_DIRS"

I hope that explanation makes sense. The directories /usr/local/share/:/usr/share/ should *always* be added to XDG_DATA_DIRS.