CURLOPT_REFERER(3) on macOS

The text bd3ab8c2d5c1, 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.

set the HTTP referer header

CURLOPT_REFERER(3) on macOS now