* keyboard.h (EVENT_HAS_PARAMETERS): Definition changed - all events

* keyboard.h (EVENT_HAS_PARAMETERS): Definition changed - all events
	are not 5 elements long.
	(EVENT_HEAD): Work correctly on all sorts of events, not just
	events with parameters.
	(EVENT_WINDOW, EVENT_BUFFER_POSN, EVENT_SCROLLBAR_BUTTON,
	EVENT_WINDOW_POSN, EVENT_TIMESTAMP): These aren't useful
	anymore; this information may appear twice in an event.  These
	are replaced by the POSN_ accessors, which are meant to be
	composed with the EVENT_START and EVENT_END accessors.
	(EVENT_START, EVENT_END): Two new accessors, to get at the
	starting and ending position of an event.
	(POSN_WINDOW, POSN_BUFFER_POSN, PONS_SCROLLBAR_BUTTON,
	POSN_WINDOW_POSN, POSN_TIMESTAMP): New macros, to futher
	diasassemble the values returned by EVENT_START and EVENT_END.

	* keyboard.h (Qevent_unmodified): Extern declaration replaced by...
	(Qevent_symbol_elements): This.
	(EVENT_HEAD_UNMODIFIED): Use the Qevent_symbol_elements
	property, rather than the Qevent_unmodified property.