Translationstring

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- Preserve default translations even if they are an empty string. This
fixes problems with Chameleon being unable to determine if a translation
is present or not.

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- Add ``__getstate__`` and ``__reduce__`` methods to translation
string to allow for pickling.

- Fix bug in ChameleonTranslate. When ``i18n:translate`` was used in
templates, a translation string was inappropriately created with a
``default`` value of the empty string. Symptom: template text would
"disappear" rather than being returned untranslated.

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- Initial release.