Poll for file descriptors

The AgsPollingThread polls your file descriptors. Since it is derived by AgsThread it runs tic based like other threads.

Call ags_polling_thread_add_poll_fd() and pass an AgsPollFd to it, in order to poll a resource. Note the resource won't be polled unless the thread was started by calling ags_thread_start(). The ::dispatch signal notifies about a ressource to be ready for Input/Output.

To stop poll a resource either remove the poll file descriptor by calling ags_polling_thread_remove_poll_fd(). Or just stop the polling thread by ags_thread_stop() so any resource won't be polled.