* intervals.c (find_interval): Doc fixes, computation of

* intervals.c (find_interval): Doc fixes, computation of
	tree->position rearranged for clarity.

	* intervals.c (find_interval): Consistently treat POSITION as an
	actual buffer position, i.e. origin 1.  The old code seemed
	undecided on this point.  Treat the end of the buffer as being
	part of the rightmost interval.
	(adjust_intervals_for_insertion): Consistently treat POSITION as
	origin 1.
	(interval_deletion_adjustment): The exception: FROM should be
	origin zero here.  Consistently treat it as such.  Simplify code
	which shrinks and possibly deletes intervals.
	(adjust_intervals_for_deletion): Treat start as origin 1; our
	caller does.
	(set_point): Use buffer positions throughout, not a mix of buffer
	posns and origin zero posns.
	(get_local_map): Remove special case for POSITION at end of buffer;
	find_interval handles that case correctly.
	(verify_interval_modification): Remove special case for START at
	end of buffer.
	* textprop.c (validate_interval_range): End-of-buffer/string
	positions no longer need special handling.

	* intervals.c (make_new_interval): #if 0 this out.  Nobody calls it.