Fix for Mac Os 10.7

src_compile:
gtkapplication-quartz-menu.c:265: error: incompatible type for argument 1 of 'roundf'
make[4]: *** [libgtk_3_la-gtkapplication-quartz-menu.lo] Error 1

More info:
https://trac.macports.org/ticket/43283
https://bugzilla.gnome.org/show_bug.cgi?id=727366
https://bugs.gentoo.org/show_bug.cgi?id=519058

--- gtk/gtkapplication-quartz-menu.c.orig	2014-05-08 01:40:39.000000000 +0200
+++ gtk/gtkapplication-quartz-menu.c	2014-05-15 11:16:09.000000000 +0200
@@ -30,6 +30,16 @@
 
 #import <Cocoa/Cocoa.h>
 
+#if !defined(MAC_OS_X_VERSION_10_7) || \
+MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_7
+
+@interface NSScreen (LionAPI)
+- (CGFloat)backingScaleFactor;
+- (NSRect)convertRectToBacking:(NSRect)aRect;
+@end
+
+#endif // 10.7
+
 #define ICON_SIZE 16
 
 #define BLACK               "#000000"
@@ -262,7 +272,7 @@
         }
 
       theme = gtk_icon_theme_get_default ();
-      scale = roundf ([[NSScreen mainScreen] backingScaleFactor]);
+      scale = [[NSScreen mainScreen] respondsToSelector:@selector(backingScaleFactor)] ? roundf ([[NSScreen mainScreen] backingScaleFactor]) : 1.;
       info = gtk_icon_theme_lookup_by_gicon_for_scale (theme, icon, ICON_SIZE, scale, GTK_ICON_LOOKUP_USE_BUILTIN);
 
       if (info != NULL)