Continue work on continuation lines. Some progress with cursor motion.

Continue work on continuation lines.  Some progress with cursor motion.

 xdisp.c (set_cursor_from_row): Don't overwrite cursor position
 if it is not a better candidate than what we already have.
 (display_line): Keep calling set_cursor_from_row for
 bidi-reordered rows even if we already have a possible candidate
 for cursor position.  Undo the row_end setting throughout the
 code, and instead do it after all the row's glyphs have been
 produced, by looping over the glyphs.