Add --no-ssh-pty option.

This eliminates issues with typeahead being echoed by the remote pty
and corrupting remote output from mosh-server to the mosh script, but
cannot be made default because older mosh-servers require a pty.

src/frontend/mosh-server.cc

@@ -388,8 +388,6 @@ static int run_server( const char *desired_ip, const char *desired_port,
   if ( ioctl( STDIN_FILENO, TIOCGWINSZ, &window_size ) < 0 ||
        window_size.ws_col == 0 ||
        window_size.ws_row == 0 ) {
-    fprintf( stderr, "Server started without pseudo-terminal. Opening 80x24 terminal.\n" );
-
     /* Fill in sensible defaults. */
     /* They will be overwritten by client on first connection. */
     memset( &window_size, 0, sizeof( window_size ) );