Add ir.message and use custom exceptions

issue3672

dunning.py

@@ -130,7 +130,7 @@ class Dunning(ModelSQL, ModelView):
         table = cls.__table__()
         cls._sql_constraints = [
             ('line_unique', Unique(table, table.line),
-                'Line can be used only once on dunning.'),
+                'account_dunning.msg_dunning_line_unique'),
             ]
         cls._active_field = 'active'
 

message.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0"?>
+<!-- This file is part of Tryton.  The COPYRIGHT file at the top level of
+this repository contains the full copyright notices and license terms. -->
+<tryton>
+    <data group="1">
+        <record model="ir.message" id="msg_dunning_line_unique">
+            <field name="text">Line can be used only once on dunning.</field>
+        </record>
+    </data>
+</tryton>

tryton.cfg

@@ -10,3 +10,4 @@ xml:
     dunning.xml
     party.xml
     account.xml
+    message.xml