Translation approval stumbles over divergence

Approving a translation message seems to break when divergence is involved (and therefore the message needs to be cloned).

The reason is that POTMsgSet._setTranslation documents its potranslations parameter as being a list of POTranslations, but in these cases it calls _makeTranslation which expects a dict.

Other call sites actually do seem to pass a dict, but _approveTranslation passes a list. We didn't notice this because it's fairly unusual for _approveTranslation to create a new message, and unit tests would pass a list instead. We should update the documentation and just use a dict in all cases.

OOPS-1839EA1279, OOPS-1839EA1302, OOPS-1839EA1310, OOPS-1839ED1147, OOPS-1839EE1253
OOPS-1839EE1270