fix changeset calculation with translated documents

it seems that translated documents are always considered changed by the changeset calculation. i guess on phpcr level this is caught as no node actually changes, so this does not lead to massive write queries.

however, when listening to events, this can create severe problems. in my case, i have a list of 80 items to chose from in an admin. those are all loaded, thus all considered changed and instead of 1 event for my changed page, i get 81 events and have no indication that only 1 really did change.
i think we would have less copies of the translated content lying around when nothing changed. i don't see how event listeners could mess with the actual translated values in the array. 

the only thing we really do need to compare at this time here are the fields of the currently loaded locale, which we do above when iterating over the fields as per metadata. i think right now we even compare the current locale twice, once as part of all fields of the document and once here. as the current locale is also in documentTranslations.

but anyway, i am fine to merge with this state. i can try to refactor afterwards unless you can convince me that this would somehow break event listeners from changing data.