[libpeas] Correctly check when there are multiple GDK backends

[Garrett Regier <gregier src gnome org>]

commit 84a46b9cc24b6cd3d81e03e02424e439a4a5fb5e
Author: Garrett Regier <garrettregier gmail com>
Date:   Thu Dec 8 12:19:32 2011 -0800

    Correctly check when there are multiple GDK backends

 configure.ac |    8 +-------
 1 files changed, 1 insertions(+), 7 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 198db40..fedaaba 100644
--- a/configure.ac
+++ b/configure.ac
@@ -127,13 +127,7 @@ dnl ================================================================
 AC_MSG_CHECKING([for native Mac OS X])
 
 
-gdk_windowing=`$PKG_CONFIG --variable=target gdk-3.0`
-
-if test "$gdk_windowing" = "quartz"; then
-	os_osx=yes
-else
-	os_osx=no
-fi
+GTK_CHECK_BACKEND([quartz], [3.0.0], [os_osx=yes], [os_osx=no])
 AC_MSG_RESULT([$os_osx])
 AM_CONDITIONAL(OS_OSX, test "$os_osx" = "yes")