[IMP] allow unreconciling bank statement lines by adding the cancel button

Since account_constraint forbids the deletion of account moves that
are linked to a bank statement, we add the possibility to delete them
from the bank statement itself, to provide a way to fix erroneous matches.

account_constraints/__openerp__.py

@@ -61,6 +61,7 @@ Summary of constraints are:
     'website': 'http://www.camptocamp.com',
     'data': [
         'view/account_journal.xml',
+        'view/account_bank_statement.xml',
     ],
     'installable': True,
 }

account_constraints/model/account_bank_statement.py

@@ -18,7 +18,7 @@
 #
 ##############################################################################
 
-from openerp import models, api
+from openerp import models, api, fields
 
 
 class AccountBankStatement(models.Model):
@@ -45,6 +45,14 @@ class AccountBankStatement(models.Model):
 class AccountBankStatementLine(models.Model):
     _inherit = "account.bank.statement.line"
 
+    state = fields.Selection(string='Statement state',
+                             related='statement_id.state')
+
+    @api.multi
+    def cancel(self):
+        self = self.with_context(from_parent_object=True)
+        return super(AccountBankStatementLine, self).cancel()
+
     @api.multi
     def process_reconciliation(self, mv_line_dicts):
         """Add the from_parent_object key in context in order to be able

account_constraints/view/account_bank_statement.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0"?>
+<openerp>
+    <data>
+        <!--
+            Since account_constraint forbids the deletion of account moves that
+            are linked to a bank statement, we add the possibility to delete them
+            from the bank statement itself, to let the user fix erroneous reconciles.
+        -->
+        <record id="bank_statement_cancel_form_inherit" model="ir.ui.view">
+            <field name="name">bank.statement.cancel.form.inherit</field>
+            <field name="model">account.bank.statement</field>
+            <field name="inherit_id" ref="account.view_bank_statement_form"/>
+            <field name="arch" type="xml">
+                <xpath expr="//field[@name='bank_account_id']" position="after">
+                    <field name="state" invisible="1"/>
+                    <button name="cancel" attrs="{'invisible': ['|', ('journal_entry_id', '=', False), ('state', '=', 'confirm')]}" string="Cancel" type="object" icon="gtk-undo"/>
+                </xpath>
+            </field>
+        </record>
+    </data>
+</openerp>