Retrospective commit from 2009-10-08.

Retrospective commit from 2009-10-08.

Finish up working on paragraph's base direction.
Start working on display of right-to-left glyph rows.
Rewrite set_cursor_from_row to support bidi.

 xdisp.c (string_buffer_position_lim): New function.
 (string_buffer_position): Most of code moved to
 string_buffer_position_lim.  Last argument and return value are
 now EMACS_INT; all callers changed.
 (set_cursor_from_row): Rewritten to support bidirectional text and
 reversed glyph rows.
 dispextern.h <string_buffer_position>: Update prototype.
 bidi.c (bidi_paragraph_init): Fix initialization of POS.
 dispextern.h (struct glyph_row): New member reversed_p.
 buffer.c (syms_of_buffer): Remove DEFVAR_LISP_NOPRO for
 default-direction-reversed, default-bidi-display-reordering, and
 default-paragraph-direction.