stop i18n stub from confusing ourself

Depending on the type of loading and unloading of scripts, our stub can confuse ourself if initialized again on the same (existing) window object. Eventually we could have negative side effects with this change, if somebody uses a i18n module w/o "init" - but that should be a rare edge case, IMHO.
Merge pull request #205 from esn303/patch-1

stop i18n stub from confusing ourself