curl_easy_duphandle(3) on macOS

The text b7898b175987, as Mac OS X 10.7.5, Mac OS X 10.7.4, Mac OS X 10.7.3, Mac OS X 10.7.2, Mac OS X 10.7.1, Mac OS X 10.7 shipped it.

Clone a libcurl session handle

curl_easy_duphandle(3) on macOS now