Fix export of translations

* Add a test which ensures that export is still feasible
* Export looks at res_id and if it is >= 0, it assumed the translation
  to belong to a model record and res_id to be the db record id.
  However, nereid uses the res_id for uniquness and lineno gets stored
  in it. This patch skips this for translations from nereid types.
Merge pull request #159 from sharoonthomas/develop

Fix export of translations