[gdm] Update GTK dependency to 2.20.0 since changes to fix bug #612472 now require interfaces added to 2.1

[Brian Cameron <bcameron src gnome org>]

commit 7ed5ce3561a5bad0df2e3549c4f98b3a1ee8d931
Author: Brian Cameron <Brian Cameron sun com>
Date:   Tue May 4 17:05:36 2010 -0500

    Update GTK dependency to 2.20.0 since changes to fix bug #612472 now require
    interfaces added to 2.19.7.

 configure.ac |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index a3f6044..617c05b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -41,7 +41,7 @@ dnl ---------------------------------------------------------------------------
 
 DBUS_GLIB_REQUIRED_VERSION=0.74
 GLIB_REQUIRED_VERSION=2.22.0
-GTK_REQUIRED_VERSION=2.12.0
+GTK_REQUIRED_VERSION=2.20.0
 PANGO_REQUIRED_VERSION=1.3.0
 SCROLLKEEPER_REQUIRED_VERSION=0.1.4
 GCONF_REQUIRED_VERSION=2.6.1