Boost asio Boost::asio — UnregisterWaitEx' has not been declared

 a) defined Windows version: added -D_WIN32_WINNT=0x0501 -DWINVER=0x0501
  for a list of Windows version: http://msdn.microsoft.com/en-us/library/windows/desktop/aa383745%28v=vs.85%29.aspx

b) To solve the "undefined reference to `WSAStartup@8'" errors, added the library wsock32  (ie: -lwsock32)