[gtk-mac-integration] Fix compile error on Leopard & Tiger.

[John Ralls <jralls src gnome org>]

commit 177e9089a4bfdb04d73a12eba6dc3b426b33b8d6
Author: John Ralls <jralls ceridwen us>
Date:   Sun Feb 22 16:15:57 2015 -0800

    Fix compile error on Leopard & Tiger.

 src/GtkApplicationDelegate.h |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/src/GtkApplicationDelegate.h b/src/GtkApplicationDelegate.h
index 8d62732..44c35fd 100644
--- a/src/GtkApplicationDelegate.h
+++ b/src/GtkApplicationDelegate.h
@@ -21,7 +21,12 @@
  */
 
 #import <Cocoa/Cocoa.h>
+#include <AvailabilityMacros.h>
 
+#if MAC_OS_X_VERSION_MIN_REQUIRED >= 1060
 @interface GtkApplicationDelegate : NSObject <NSApplicationDelegate> {}
+#else
+ interface GtkApplicationDelegate : NSObject {}
+#endif
 @end