curl_free(3) on macOS

The text aa4fa81121ed, 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.

reclaim memory that has been obtained through a libcurl call

curl_free(3) on macOS now