Retrospective commit from 2009-09-27.

Retrospective commit from 2009-09-27.

Support character mirroring.
Support iteration that starts in the middle of a line.
Misc cleanups.

 xdisp.c (next_element_from_buffer): If called not at line
 beginning, start bidi iteration from line beginning.
 bidi.c (bidi_paragraph_init): Use
 bidi_overriding_paragraph_direction instead of a literal zero.
 (bidi_initialize): Fix some character types, per Unicode 5.x.
 (bidi_get_type): Abort if called with invalid character code.
 dispextern.h: Add prototype of bidi_mirror_char.
 xdisp.c (get_next_display_element): Mirror characters whose
 resolved type is STRONG_R.