CURLOPT_FTP_USE_EPRT(3) on macOS

The text 6bbe480f5f0b, 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.

enable/disable use of EPRT with FTP