Fix cursor motion across display strings covering reordered text.
src/xdisp.c (set_cursor_from_row): Set start and stop points
according to the row's direction when priming the loop that looks
for the glyph on which to display cursor.
(single_display_spec_intangible_p): Function deleted.
(display_prop_intangible_p): Reimplement to call
handle_display_spec instead of single_display_spec_intangible_p.
Accept 3 additional arguments needed by handle_display_spec. This
fixes incorrect cursor motion across display property with complex
values: lists, `(when COND...)' forms, etc.
(single_display_spec_string_p): Support property values that are
lists with the argument STRING its top-level element.
(display_prop_string_p): Fix the condition for processing a
property that is a list to be consistent with handle_display_spec.
src/keyboard.c (adjust_point_for_property): Adjust the call to
display_prop_intangible_p to its new signature.
src/dispextern.h (display_prop_intangible_p): Adjust prototype.