[gdm] gdm-{wayland, x}-session: omit GNOME_SHELL_SESSION_MODE from environment

[Ray Strode <halfline src gnome org>]

commit 853e93be31519e143cb2bcf00d12a32f789da83f
Author: Xiaoguang Wang <xwang suse com>
Date:   Mon Aug 7 14:26:08 2017 +0800

    gdm-{wayland,x}-session: omit GNOME_SHELL_SESSION_MODE from environment
    
    After a user logs out, the systemd --user session may still be running
    (if, say, the user session was left around in the closing state,
    because of pulseaudio).
    
    If that happens, new user sessions will inherit the environment of
    previous sessions.  Some of these environment variables are already
    intentionally pruned, DISPLAY, XAUTHORITY, WAYLAND_SOCKET, etc.  One
    environment variable that isn't pruned, but should be, is
    GNOME_SHELL_SESSION_MODE.
    
    If it lingers, users could end up in classic mode even though they
    picked the non-classic mode from the gear menu.
    
    This commit adds GNOME_SHELL_SESSION_MODE to the list of environment
    variables to prune.
    
    (minor changes to original patch and commit message from Ray Strode)
    
    https://bugzilla.gnome.org/show_bug.cgi?id=785918

 daemon/gdm-wayland-session.c |    1 +
 daemon/gdm-x-session.c       |    1 +
 2 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/daemon/gdm-wayland-session.c b/daemon/gdm-wayland-session.c
index af79608..b648e9d 100644
--- a/daemon/gdm-wayland-session.c
+++ b/daemon/gdm-wayland-session.c
@@ -284,6 +284,7 @@ spawn_session (State        *state,
                                                     "XAUTHORITY",
                                                     "WAYLAND_DISPLAY",
                                                     "WAYLAND_SOCKET",
+                                                    "GNOME_SHELL_SESSION_MODE",
                                                     NULL };
 
         g_debug ("Running wayland session");
diff --git a/daemon/gdm-x-session.c b/daemon/gdm-x-session.c
index b5c0d20..88fe96f 100644
--- a/daemon/gdm-x-session.c
+++ b/daemon/gdm-x-session.c
@@ -609,6 +609,7 @@ spawn_session (State        *state,
                                                      "XAUTHORITY",
                                                      "WAYLAND_DISPLAY",
                                                      "WAYLAND_SOCKET",
+                                                     "GNOME_SHELL_SESSION_MODE",
                                                      NULL };
 
         g_debug ("Running X session");