Retrospective commit from 2009-1219.

Retrospective commit from 2009-1219.

Fix reordering of Arabic text in etc/HELLO.
Extend .gdbinit commands to support bidirectional display.

 buffer.c (Fbuffer_swap_text): Swap the values of
 bidi_display_reordering and bidi_paragraph_direction.

 bidi.c (bidi_resolve_weak): Fix nesting of conditions for Wn
 processing.  Move W3 after W1 and W2.  Simplify W4 because it is
 now always after W1.

 .gdbinit (pbiditype): New command.
 (pgx): Use it to display bidi level and type of the glyph.