GIO: Add G-I annotations for several methods

Specifically:
 - g_io_stream_get_input/output_stream()
 - g_socket_client_get_local_address()
 - g_socket_connection_get_socket()
 - g_socket_listener_add_address()
 - g_socket_listener_accept_socket()
 - g_socket_listener_accept()
 - g_io_extension_point_get_extensions()
5 files changed