Richard Atterer brought a patch that added support for SOCKS4a proxies, which

is an inofficial PROXY4 variant that sends the hostname to the proxy instead
of the resolved address (which is already supported by SOCKS5).  --socks4a is
the curl command line option for it and CURLOPT_PROXYTYPE can now be set to
CURLPROXY_SOCKS4A as well.