sql: add d.date to GROUP BY to comply with Postgresql 8.4

Postgresql 9.1 is able to infer that d.date depends on d.id

docbow_project/docbow/sql.py

@@ -49,7 +49,7 @@ GET_UNSEEN_DOCUMENTS_SQL = '''SELECT d.id
     LEFT JOIN docbow_seendocument as sd
         ON sd.document_id = d.id AND sd.user_id = %s
     WHERE sd.id IS NULL
-    GROUP BY d.id
+    GROUP BY d.id, d.date
     ORDER BY d.date
     '''
 
@@ -57,7 +57,7 @@ GET_DOCUMENTS_SQL = '''SELECT d.id
     FROM docbow_document AS d
     INNER JOIN docbow_mailbox AS mb ON 
         mb.document_id = d.id and mb.owner_id IN %s
-    GROUP BY d.id 
+    GROUP BY d.id, d.date
     ORDER BY d.date'''
 
 SEEN_DOCUMENT = '''SELECT COUNT(*) > 0