Log Message:
Update libdatrie to 0.2.8.

0.2.8 (2014-01-10)
=====
- Fix compiler warnings in test suites.
- Fix edge-case error on alphabet set of size 255.
  (Thanks Naoki Youshinaga for the report, test case, and analysis.)
- Fail trie operations on non-alphabet inputs, rather than silently allowing
  them to sneak in as false keys.
  (Thanks Naoki Youshinaga for the suggestion.)
- Improved documentation.

0.2.7.1 (2013-10-22)
=======
- Bump library versioning to reflect API addition.
  (Change missing in previous release)

0.2.7 (2013-10-21)
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- Fix portability issue with non-GCC compilers.
  [Thanks Gabi Daver for the report and fix (via Mikhail Korobov).]
- Fix compiler warnings.
- New utility API for comparing AlphaChar strings.
- Add test suites.
- Update doxygen doc generation.