message: Implement http_reachability without AFNetworking
  Use SCNetworkReachabilityCreateWithName() and
  SCNetworkReachabilityGetFlags() directly.
diff: @@ -251,22 +251,30 @@ class http_reachability::impl
  public:
  impl(const std::string& url)
  {
  - NSString *str = str::to_NS(url);
  - m_native = [[AFHTTPClient alloc] initWithBaseURL:[NSURL URLWithString:str]];
  + NSString *host = [[NSURL URLWithString:str::to_NS(url)] host];
  + m_nr = SCNetworkReachabilityCreateWithName(kCFAllocatorDefault, [host UTF8String]);
  }
  ~impl()
  {
  - m_native = nil;
  + if (m_nr)
  + {
  + SCNetworkReachabilityUnscheduleFromRunLoop(m_nr, CFRunLoopGetMain(), kCFRunLoopCommonModes);
  + CFRelease(m_nr);
  + }
  }
  bool is_reachable() const
  {
  - return m_native.networkReachabilityStatus != AFNetworkReachabilityStatusNotReachable;
  + SCNetworkReachabilityFlags flags;
  + if (m_nr && SCNetworkReachabilityGetFlags(m_nr, &flags))
  + return (flags & kSCNetworkReachabilityFlagsReachable) != 0;
  +
  + return true; // fallback assumption
  }
  private:
  - AFHTTPClient *m_native;
  + SCNetworkReachabilityRef m_nr;
  };
  