Added another way to subclass CPDocumentController

Tests/Manual/CPDocumentControllerTest/withoutNib/DocumentController.j

@@ -0,0 +1,15 @@
+@import <AppKit/CPDocumentController.j>
+@import <AppKit/CPAlert.j>
+
+@implementation DocumentController : CPDocumentController
+{
+}
+
+- (id)init
+{
+    self = [super init];
+
+    return self;
+}
+
+@end