improve implementation of ftp object handles * urlwrite.cc (curl_handles): Delete class. (handles): Delete static variable. (ch_manager): New class. (make_handle_fraction): New function. (F__ftp_pwd__, F__ftp_cwd__, F__ftp_dir__, F__ftp_ascii__, F__ftp_binary__, F__ftp_mode__, F__ftp_delete__, F__ftp_rmdir__, F__ftp_mkdir__, F__ftp_rename__, F__ftp_mput__, F__ftp_mget__): Find curl object corresponding to given handle using ch_manager instead of looking in handles map. (F__ftp__): Return handle instead of accepting it as argument. Change all uses.