[gtk+] Add a note to gdk_screen_get_width/height_mm

[Matthias Clasen <matthiasc src gnome org>]

commit b437f89c052e5d1a0bfc5521efc1eeedd4ad3f28
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Aug 15 22:20:16 2015 -0400

    Add a note to gdk_screen_get_width/height_mm
    
    The values returned by these functions are not very well defined,
    recommend to use the monitor dimensions instead.

 gdk/gdkscreen.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/gdk/gdkscreen.c b/gdk/gdkscreen.c
index 146e5af..4949022 100644
--- a/gdk/gdkscreen.c
+++ b/gdk/gdkscreen.c
@@ -619,7 +619,10 @@ gdk_screen_get_height (GdkScreen *screen)
  * @screen: a #GdkScreen
  *
  * Gets the width of @screen in millimeters.
- * Note that on some X servers this value will not be correct.
+ *
+ * Note that this value is somewhat ill-defined when the screen
+ * has multiple monitors of different resolution. It is recommended
+ * to use the monitor dimensions instead.
  *
  * Returns: the width of @screen in millimeters.
  *
@@ -638,7 +641,10 @@ gdk_screen_get_width_mm (GdkScreen *screen)
  * @screen: a #GdkScreen
  *
  * Returns the height of @screen in millimeters.
- * Note that on some X servers this value will not be correct.
+ *
+ * Note that this value is somewhat ill-defined when the screen
+ * has multiple monitors of different resolution. It is recommended
+ * to use the monitor dimensions instead.
  *
  * Returns: the heigth of @screen in millimeters.
  *