Retrospective commit from 2009-12-26.

Retrospective commit from 2009-12-26.

Redesign handle_stop_backwards.
Fix character mirroring for non-ASCII characters.

 xdisp.c (handle_stop_backwards): Call compute_stop_pos in the
 loop, instead of calling handle_stop.  Call handle_stop only once,
 after the loop.
 (next_element_from_buffer): Don't call handle_stop_backwards if at
 stop position.  If base_level_stop is zero, set it to 1.

 term.c (append_glyph): Fill resolved_level and bidi_type slots
 of struct glyph for unidirectional display.

 xdisp.c (set_cursor_from_row): Handle zero-width characters.

 bidi.c (bidi_mirror_char): More efficient code (suggested by
 Ehud Karni <ehud@unix.mvs.co.il>).  Don't even try to mirror
 non-ASCII characters.