Store raw data as given in VPOExport.column_names.
def
setRefs(self, pofile, potmsgsets_lookup):
Store various object references.
:param pofile: the `POFile` that this export is for.
:param potmsgsets_lookup: a dict mapping numeric ids to `POTMsgSet`s.
This saves the ORM the job of fetching them one by one as other
objects refer to them.