Michal Marek introduced CURLOPT_PROXY_TRANSFER_MODE which is used to control

the appending of the "type=" thing on FTP URLs when they are passed to a
HTTP proxy. Some proxies just don't like that appending (which is done
unconditionally in 7.17.1), and some proxies treat binary/ascii transfers
better with the appending done!

include/curl/curl.h

@@ -1182,6 +1182,9 @@ typedef enum {
   /* POST volatile input fields. */
   CINIT(COPYPOSTFIELDS, OBJECTPOINT, 165),
 
+  /* set transfer mode (;type=<a|i>) when doing FTP via an HTTP proxy */
+  CINIT(PROXY_TRANSFER_MODE, LONG, 166),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;