curl_easy_perform(3) on macOS

The text 13c6313161a2, as OS X 10.11.6, OS X 10.11.5, OS X 10.11.4, OS X 10.11.3, OS X 10.11.2, OS X 10.11.1, OS X 10.11, OS X 10.10.5 shipped it.

perform a blocking file transfer

curl_easy_perform(3) on macOS now