Fix exponential slowdowns on repeated tty frame creation.

Fix exponential slowdowns on repeated tty frame creation.

* lisp/term/xterm.el: Protect extended function-key-map from being added
  to the real function-key-map each time the file is loaded.
  (xterm-function-map): New variable.

* lisp/term/rxvt.el: Ditto.
  (rxvt-function-map): New variable.

* lisp/term/lk201.el: Add note on buggy globalness of define-key.
* lisp/term/iris-ansi.el: Ditto.
* lisp/term/news.el: Ditto.
* lisp/term/sun.el: Ditto.

git-archimport-id: lorentey@elte.hu--2004/emacs--multi-tty--0--patch-337