Implement extra_keyboard_modifiers properly.

Implement extra_keyboard_modifiers properly.
	* keyboard.c (syms_of_keyboard): Doc fix for
	extra-keyboard-modifiers; use the same modifier bits as we do for
	characters.
	(read_char): Apply all the modifiers in extra_keyboard_modifiers
	to the input characters, so you can get hyper, super, and the rest
	of the gang.
	* xterm.c (x_emacs_to_x_modifiers): New function.
	(x_convert_modifiers): Renamed to x_x_to_emacs_modifiers, for
	consistency.  Callers changed.
	(XTread_socket): Apply x_emacs_to_x_modifiers to
	extra_keyboard_modifiers before setting the state member of the
	event; this will get all the modifiers on ASCII characters.

	* xterm.c (x_text_icon): Don't call XSetIconName; it should be
	unnecessary, and perhaps it's killing the icon pixmap.