Log Message:
Update to 0.9.26:

Overview of changes leading to 0.9.26
Thursday, January 30, 2014
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- Misc fixes.
- Fix application of 'rtlm' feature.
- Automatically apply frac/numr/dnom around U+2044 FRACTION SLASH.
- New header: hb-ot-shape.h
- Uniscribe: fix scratch-buffer accounting.
- Reorder Tai Tham SAKOT to after tone-marks.
- Add Hangul shaper.
- New files:
  hb-ot-shape-complex-hangul.cc
  hb-ot-shape-complex-hebrew.cc
  hb-ot-shape-complex-tibetan.cc
- Disable 'cswh' feature in Arabic shaper.
- Coretext: better handle surrogate pairs.
- Add HB_TAG_MAX and _HB_SCRIPT_MAX_VALUE.