conditionally define NSAppKitVersionNumber constants in pch, properly…

… conditionalise Obj-C code

Sparkle.pch

@@ -6,11 +6,25 @@
 //  Copyright 2008 Andy Matuschak. All rights reserved.
 //
 
+#ifndef NSAppKitVersionNumber10_4
+#define NSAppKitVersionNumber10_4 824
+#endif
+
+#ifndef NSAppKitVersionNumber10_5
+#define NSAppKitVersionNumber10_5 949
+#endif 
+
+#ifndef NSAppKitVersionNumber10_6
+#define NSAppKitVersionNumber10_6 1038
+#endif 
+
+#ifdef __OBJC__
+
 #define SPARKLE_BUNDLE [NSBundle bundleWithIdentifier:@"org.andymatuschak.Sparkle"]
 #define SULocalizedString(key,comment) NSLocalizedStringFromTableInBundle(key, @"Sparkle", SPARKLE_BUNDLE, comment)
 #define SUAbstractFail() NSAssert2(nil, @"Can't call %@ on an instance of %@; this is an abstract method!", __PRETTY_FUNCTION__, [self class]);
 
-#ifdef __OBJC__
 #import <Cocoa/Cocoa.h>
 #import "SUConstants.h"
+
 #endif