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!

lib/urldata.h

@@ -1439,6 +1439,8 @@ struct UserDefined {
                             content-encoded (chunked, compressed) */
   long new_file_perms;    /* Permissions to use when creating remote files */
   long new_directory_perms; /* Permissions to use when creating remote dirs */
+  bool proxy_transfer_mode; /* set transfer mode (;type=<a|i>) when doing FTP
+                               via an HTTP proxy */
 
   char *str[STRING_LAST]; /* array of strings, pointing to allocated memory */
 };