* lisp/term/rxvt.el: Enable backeted paste and window title

* lisp/term/rxvt.el: Enable backeted paste and window title

rxvt-unicode uses the same escape sequences as xterm so just re-use
the xterm functions to enable them.  The `xterm-rxvt-function-map`
keymap already has

    (define-key map "\e[200~" [xterm-paste])

so we're already handling the paste sequence and only need to enable it.
Tested on rxvt-unicode version 9.22.

(rxvt-set-window-title): New var.
(terminal-init-rxvt): Use it; enable bracketed paste mode;
run terminal-init-rxvt-hook.