https://bugzilla.novell.com/show_bug.cgi?id=332917 about a HTTP redirect to
FTP that caused memory havoc. His work together with my efforts created two
fixes:

#1 - FTP::file was moved to struct ftp_conn, because is has to be dealt with
     at connection cleanup, at which time the struct HandleData could be
     used by another connection.
     Also, the unused char *urlpath member is removed from struct FTP.

#2 - provide a Curl_reset_reqproto() function that frees
     data->reqdata.proto.* on connection setup if needed (that is if the
     SessionHandle was used by a different connection).