Log Message:
Update to 0.9.21:

Overview of changes leading to 0.9.21
Monday, September 16, 2013
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- Rename gobject-introspection library name from harfbuzz to HarfBuzz.
- Remove (long disabled) hb-old and hb-icu-le test shapers.
- Misc gtk-doc and gobject-introspection annotations.
- Misc fixes.
- API changes:

  * Add HB_SET_VALUE_INVALID