AFNetworking 2.0 当Deployment Target 低于6.0时，AFURLConnectionOperation.h,AFURLSessionManager.h
@property(nonatomic, strong) dispatch_queue_t completionQueue;
由于sdk低于6.0时，dispatch_queue_t ARC没有托管，出现提示错误
Property with ‘retain (or strong)‘attribute must be of object type
修改为
/**
Thedispatch queue for `completionBlock`. If `NULL` (default), the main queue isused.
*/
// modify by dai date: 2014/05/22
#if OS_OBJECT_USE_OBJC
@property (nonatomic, strong)dispatch_queue_t completionQueue;
#else
@property (nonatomic, assign) dispatch_queue_tcompletionQueue;
#endif
/**
Thedispatch group for `completionBlock`. If `NULL` (default), a private dispatchgroup is used.
*/
#if OS_OBJECT_USE_OBJC
@property (nonatomic, strong) dispatch_group_tcompletionGroup;
#else
@property (nonatomic, assign) dispatch_group_tcompletionGroup;
#endif