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.
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.