Added missing file

Core/Source/DTWeakSupport.h

@@ -0,0 +1,33 @@
+//
+//  DTWeakSupport.h
+//  DTFoundation
+//
+//  Created by Oliver Drobnik on 6/3/13.
+//  Copyright (c) 2013 Cocoanetics. All rights reserved.
+//
+
+/**
+ Useful defines for building code the compiles with zeroing weak references if the deployment target allows it. This is possible from minimum supported iOS 5.0 and OS X 10.7 and above. Note that on OS X 10.7 some AppKit classes do not support having a weak ref, e.g. NSWindowController or NSViewController.
+*/
+
+#import <Availability.h>
+
+#if __has_feature(objc_arc_weak)
+
+	// zeroing weak refs are supported for ivars and properties
+	#define DT_WEAK_VARIABLE __weak
+	#define DT_WEAK_PROPERTY weak
+
+#elif __has_feature(objc_arc)
+
+	/// zeroing weak refs not supported, fall back to unsafe unretained and assigning
+	#define DT_WEAK_VARIABLE __unsafe_unretained
+	#define DT_WEAK_PROPERTY assign
+
+#else
+
+	// define something, as this header might be included in a non-ARC project for using compiled code from an ARC static lib
+	#define DT_WEAK_VARIABLE
+	#define DT_WEAK_PROPERTY assign
+
+#endif