CURLOPT_RTSP_REQUEST(3) on macOS

The text 98813c1cd83c, as macOS 10.12.5, macOS 10.12.4, macOS 10.12.3, macOS 10.12.2, macOS 10.12.1, macOS 10.12 shipped it.

specify RTSP request

CURLOPT_RTSP_REQUEST(3) on macOS now