i18n: make !TranslationsProxy activation more robust.
i18n: make !TranslationsProxy activation more robust.

In particular, if a !NullTranslations is returned by `Translations.load`, don't use it, as it doesn't support all the methods of a `babel.support.Translations` class.


git-svn-id: eda3d06fcef731589ace1b284159cead3416df9b@8495 af82e41b-90c4-0310-8c96-b1721e28e2e2

walty8/trac,jun66j5/trac-ja,netjunki/trac-Pygit2,walty8/trac,netjunki/trac-Pygit2,netjunki/trac-Pygit2,walty8/trac,jun66j5/trac-ja,jun66j5/trac-ja,jun66j5/trac-ja,walty8/trac