Don't change the global function-key-map anny more.

Don't change the global function-key-map anny more.
(xterm-mouse-mode): Use terminal-init-xterm-hook.  Don't use
after-make-frame-functions now that term/xterm.el calls us directly.
(turn-on-xterm-mouse-tracking, turn-off-xterm-mouse-tracking):
Use turn-*-xterm-mouse-tracking-on-terminal.  Only once per terminal.
(turn-on-xterm-mouse-tracking-on-terminal): Make param optional.
Setup input-decode-map and remember that xterm-mouse-mode was
enabled in this terminal.
(turn-off-xterm-mouse-tracking-on-terminal): Only disable on those
terminals where it has been enabled.