Use BidiMirroring.txt for mirroring characters in bidi context.

Use BidiMirroring.txt for mirroring characters in bidi context.

 admin/unidata/bidimirror.awk: New file.
 admin/unidata/BidiMirroring.txt: New file from
 http://www.unicode.org/Public/6.0.0/ucd/BidiMirroring-6.0.0d1.txt.
 admin/unidata/Makefile.in: (../../src/bidimirror.h): New target.
 (all): Depend on ../../src/biditype.h and ../../src/bidimirror.h.
 admin/unidata/makefile.w32-in (../../src/bidimirror.h): New target.
 (all): Depend on ../../src/biditype.h and ../../src/bidimirror.h.
 src/makefile.w32-in ($(BLD)/bidi.$(O)): Depend on biditype.h and
 bidimirror.h.
 src/deps.mk (bidi.o): Depend on biditype.h and bidimirror.h.
 src/bidi.c (bidi_initialize): Initialize bidi_mirror_table.
 (bidi_mirror_char): Use bidi_mirror_table.