[mutter] configure: Require Cogl 1.15.6

[Rico Tzschichholz <ricotz src gnome org>]

commit 54d18c0196a9cb4f88e1ff53610e51e00954838a
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Thu Aug 22 08:10:16 2013 +0200

    configure: Require Cogl 1.15.6
    
    Needed for cogl_offscreen_new_with_texture

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 37319db..7ea4930 100644
--- a/configure.ac
+++ b/configure.ac
@@ -74,7 +74,7 @@ MUTTER_PC_MODULES="
    gsettings-desktop-schemas >= 3.7.3
    xcomposite >= 0.2 xfixes xrender xdamage xi >= 1.6.0
    $CLUTTER_PACKAGE >= 1.14.3
-   cogl-1.0 >= 1.13.3
+   cogl-1.0 >= 1.15.6
    upower-glib > 0.9.11
    gnome-desktop-3.0
 "