curl_formget(3) on macOS

The text 4dd8c0958c28, 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.

serialize a previously built multipart/formdata HTTP POST chain

curl_formget(3) on macOS now