Important backwards compatible change for iOS 6 support

This commit will break the code, on purpose. Please read the important
note around the #error and fix it accordingly for iOS 6 if you can, if
not, comment it out!

OpenUDID.m

@@ -3,7 +3,7 @@
 //  openudid
 //
 //  initiated by Yann Lechelle (cofounder @Appsfire) on 8/28/11.
-//  Copyright 2011 OpenUDID.org
+//  Copyright 2011, 2012 OpenUDID.org
 //
 //  Initiators/root branches
 //      iOS code: https://github.com/ylechelle/OpenUDID
@@ -42,6 +42,8 @@
     // https://img.skitch.com/20120717-g3ag5h9a6ehkgpmpjiuen3qpwp.png
 #endif
 
+#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v)  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)
+
 #import "OpenUDID.h"
 #import <CommonCrypto/CommonDigest.h> // Need to import for CC_MD5 access
 #if TARGET_OS_IPHONE || TARGET_IPHONE_SIMULATOR
@@ -56,6 +58,7 @@
 //#define OpenUDIDLog(fmt, ...) NSLog((@"[Line %d] " fmt), __LINE__, ##__VA_ARGS__);
 
 static NSString * kOpenUDIDSessionCache = nil;
+static NSString * const kOpenUDIDDescription = @"OpenUDID_with_iOS6_Support";
 static NSString * const kOpenUDIDKey = @"OpenUDID";
 static NSString * const kOpenUDIDSlotKey = @"OpenUDID_slot";
 static NSString * const kOpenUDIDAppUIDKey = @"OpenUDID_appUID";
@@ -115,14 +118,45 @@ + (NSString*) _generateFreshOpenUDID {
     NSString* _openUDID = nil;
 
     // August 2011: One day, this may no longer be allowed in iOS. When that is, just comment this line out.
-    // March 25th 2012: this day has come, let's remove this "outlawed" call... 
+    // March 25th 2012: this day has come, let's remove this "outlawed" call...
+    // August 2012: well, perhaps much ado about nothing; in any case WWDC2012 gave us something to work with; read below
 #if TARGET_OS_IPHONE	
 //    if([UIDevice instancesRespondToSelector:@selector(uniqueIdentifier)]){
 //        _openUDID = [[UIDevice currentDevice] uniqueIdentifier];
 //    }
 #endif
+
+    //
+    // !!!!! IMPORTANT README !!!!!
+    //
+    // August 2012: iOS 6 introduces new APIs that help us deal with the now deprecated [UIDevice uniqueIdentifier]
+    // Since iOS 6 is still pre-release and under NDA, the following piece of code is meant to produce an error at
+    // compile time. Accredited developers integrating OpenUDID are expected to review the iOS 6 release notes and
+    // documentation, and replace the underscore ______ in the last part of the selector below with the right
+    // selector syntax as described here (make sure to use the right one! last word starts with the letter "A"):
+    // https://developer.apple.com/library/prerelease/ios/#documentation/UIKit/Reference/UIDevice_Class/Reference/UIDevice.html
+    //
+    // The semantic compiler warnings are still normal if you are compiling for iOS 5 only since Xcode will not
+    // know about the two instance methods used on that line; the code running on iOS will work well at run-time.
+    // Either way, it's time that you junped on the iOS 6 bandwagon and start testing your code on iOS 6 ;-)
+    //
+    // WHAT IS THE SIGNIFICANCE OF THIS CHANGE?
+    //
+    // Essentially, this means that OpenUDID will keep on behaving the same way as before for existing users or
+    // new users in iOS 5 and before. For new users on iOS 6 and after, the new official public APIs will take over.
+    // OpenUDID will therefore be obsoleted when iOS reaches significant adoption, anticipated around mid-2013.
+
+
+#if TARGET_OS_IPHONE
+    if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"6.0")) {
+        _openUDID = [[[UIDevice currentDevice] identifierForA_______] UUIDString];
+# error                                                         ^ read comments above, fix accordingly, and remove this #error line
+    }
+#endif
+
+
     // Next we generate a UUID.
-    // UUIDs (Universally Unique Identifiers), also known as GUIDs (Globally Unique Identifiers) or IIDs 
+    // UUIDs (Universally Unique Identifiers), also known as GUIDs (Globally Unique Identifiers) or IIDs
     // (Interface Identifiers), are 128-bit values guaranteed to be unique. A UUID is made unique over 
     // both space and time by combining a value unique to the computer on which it was generated—usually the
     // Ethernet hardware address—and a value representing the number of 100-nanosecond intervals since 
@@ -181,13 +215,14 @@ + (NSString*) valueWithError:(NSError **)error {
 
     // The AppUID will uniquely identify this app within the pastebins
     //
-    NSString * appUID = (NSString *) [defaults objectForKey:kOpenUDIDAppUIDKey];
+    NSString * appUID = [defaults objectForKey:kOpenUDIDAppUIDKey];
     if(appUID == nil)
     {
       // generate a new uuid and store it in user defaults
-      CFUUIDRef uuid = CFUUIDCreate(NULL);
-      appUID = (NSString *) CFUUIDCreateString(NULL, uuid);
-      CFRelease(uuid);
+        CFUUIDRef uuid = CFUUIDCreate(NULL);
+        appUID = (NSString *) CFUUIDCreateString(NULL, uuid);
+        CFRelease(uuid);
+        [appUID autorelease];
     }
 
     NSString* openUDID = nil;