[gtk+] Mention GDK_BACKEND in the docs

[Matthias Clasen <matthiasc src gnome org>]

commit 3973ef760e79e684f6e0597ac7a5ac5d451f37d4
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Dec 22 01:32:18 2010 -0500

    Mention GDK_BACKEND in the docs

 gdk/gdkdisplaymanager.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/gdk/gdkdisplaymanager.c b/gdk/gdkdisplaymanager.c
index 97022d5..829083a 100644
--- a/gdk/gdkdisplaymanager.c
+++ b/gdk/gdkdisplaymanager.c
@@ -156,6 +156,11 @@ gdk_display_manager_get_property (GObject      *object,
  *
  * Gets the singleton #GdkDisplayManager object.
  *
+ * When called for the first time, this function consults the
+ * <envar>GDK_BACKEND</envar> to find out which of the supported
+ * GDK backends to use (in case GDK has been compiled with multiple
+ * backends).
+ *
  * Returns: (transfer none): The global #GdkDisplayManager singleton;
  *     gdk_parse_pargs(), gdk_init(), or gdk_init_check() must have
  *     been called first.