open_fd
Description:
Open a connection using fd as the transport.
 If fd refers to a TCP connection, it is recommended to use vnc_display_open_fd_with_hostname instead, to provide the remote 
      hostname. This allows use of x509 based authentication which requires a hostname to be available.
Parameters:
| this | the VNC display widget | 
| fd | file descriptor to use for the connection | 
Returns:
| TRUE if a connection was opened, FALSE if already open |