* buffer.h (struct buffer): New member word_wrap.

* buffer.h (struct buffer): New member word_wrap.

* buffer.c (syms_of_buffer): New variables default-word-wrap and
word-wrap.
(init_buffer_once): Initialize them.

* dispextern.h (struct it): Replace bool truncate_lines_p with a
line_wrap enum possessing three possible values.

* termopts.h: Replace truncate_partial_width_windows with
Vtruncate_partial_width_windows.

* dispnew.c (direct_output_for_insert): Avoid direct output when
inserting a space with word wrap on.

* indent.c (compute_motion): Obey integer values of
truncate-partial-width-windows.

* xdisp.c (Vtruncate_partial_width_windows): New Lisp_Object,
replacing truncate_partial_width_windows.
(init_iterator): If Vtruncate_partial_width_windows is an integer,
truncate only if the window width is below that integer.
(start_display. resize_mini_window, produce_stretch_glyph)
(display_string, move_it_in_display_line_to): Use line_wrap.
(back_to_previous_visible_line_start, reseat_1): Reset
string_from_display_prop_p.
(display_line): Extend default face to end of line when wrapping.
(display_line, move_it_in_display_line_to): Add ability
to wrap continued lines at word boundaries.