Added support for BS2000, and for raw ftp

Added support for BS2000, and for raw ftp
login commands (needed in some circumstances).
(ange-ftp-raw-login): New custom var.
(ange-ftp-normal-login): Perform login with raw ftp commands, if
ange-ftp-raw-login is set and account password is needed.
(ange-ftp-host-type, ange-ftp-guess-host-type): Handle BS2000 hosts.
(ange-ftp-bs2000-filename-pubset-regexp)
(ange-ftp-bs2000-filename-username-regexp)
(ange-ftp-bs2000-filename-prefix-regexp)
(ange-ftp-bs2000-name-template): New consts.
(ange-ftp-bs2000-short-filename-regexp)
(ange-ftp-bs2000-fix-name-regexp-reverse)
(ange-ftp-bs2000-fix-name-regexp): New consts.
(ange-ftp-bs2000-special-prefix): New custom var.
(ange-ftp-fix-name-for-bs2000)
(ange-ftp-fix-dir-name-for-bs2000): New funs.
(ange-ftp-bs2000-host-regexp, ange-ftp-bs2000-posix-host-regexp)
(ange-ftp-bs2000-posix-hook-installed): New vars.
(ange-ftp-parse-bs2000-filename, ange-ftp-parse-bs2000-listing)
(ange-ftp-bs2000-host, ange-ftp-bs2000-posix-host)
(ange-ftp-add-bs2000-host, ange-ftp-add-bs2000-posix-host): New funs.
(ange-ftp-bs2000-filename-regexp): New const.
(ange-ftp-bs2000-additional-pubsets): New custom var.
(ange-ftp-bs2000-cd-to-posix): New fun.