Log Message:
Update xetex to 0.9999.3

Changes:
* Fix bug with extensible accents resulting in invalid glyph id some times.
* Fix alternate index in multiple alternates features to be start from zero
  like pre-0.9999 XeTeX.
* Document multiple alternates syntax in the reference documentation.
* Fix regression in \XeTeXOT* primitives with fonts where the number of
  languages in a given script is not the same in both GSUB and GPOS tables.
* Add a workaround for a bug in clang headers to allow building with it on Mac.
* Fix regression in loading PNG files on Mac.
* Fix multiple regression with vertical text layout.
* Update to HarfBuzz 0.9.15 fixing a couple of regressions with Arabic non
  spacing marks and Hangul jamo.
* Various build fixes for third party libraries.
* XeTeX reference is now included in the release tarball.
* Fix loading font files on PPC Mac OS 10.5 (and potentially other versions of
  Mac).
* Fix handling of ‘script’ and ‘language’ font options to be \ 
treated again as
  OpenType not ISO tags, so that passing version 2 Indic script tags works
  (though this is generally not needed as HarfBuzz will always use version 2
  shaping if the font has it, regardless of the tag used).
* Fix loading JPEG images that do not specify a resolution.
* When printing multi-byte characters to log or terminal avoid inserting new
  lines in the middle of the characters, and count the characters not the bytes
  when calculating line length.
* Update to HarfBuzz 0.9.14, a couple of Indic and Hangul shaping bugs.
* Port OpenType layout from ICU LayoutEngine to HarfBuzz.
* Port Graphite layout to from SilGraphite to HarfBuzz and Graphite2.
* Port AAT font layout and font searching on Mac from the deprecated ATS/ATSUI
  to Core Text, and image support on Mac from QuickTime to ImageIO framework.
  XeTeX can be finally built on 64-bit Mac! Work contributed by Jiang Jiang.