Impacted versions: 9.0, 9.0 enterprise

Steps to reproduce:
On current runbot duplicate any posted journal entry which is balanced

Current behavior:
Error message "Cannot create unbalanced entry" is shown

Expected behavior:
New Journal entry is created in state 'draft'

Video/Screenshot link (optional):
![selection_268](https://cloud.githubusercontent.com/assets/14974044/15007437/41f45a56-11d9-11e6-84f3-b297befaa521.png)

addons/account/models/account_move.py
for line in self:
            if (line.amount_currency and not line.currency_id):
                raise UserError(_("You cannot create journal items with a secondary currency without filling both 'currency' and 'amount currency' field."))
    @api.multi
    @api.constrains('amount_currency')
    def _check_currency_amount(self):
        for line in self:
            if line.amount_currency:
                if (line.amount_currency > 0.0 and line.credit > 0.0) or (line.amount_currency < 0.0 and line.debit > 0.0):
                    raise UserError(_('The amount expressed in the secondary currency must be positive when account is debited and negative when account is credited.'))
    
    
    
    @api.model
    def get_data_for_manual_reconciliation_widget(self, partner_ids, account_ids):
        """ Returns the data required for the invoices & payments matching of partners/accounts.
            If an argument is None, fetch all related reconciliations. Use [] to fetch nothing.
        """
        return {
            'customers': self.get_data_for_manual_reconciliation('partner', partner_ids, 'receivable'),
            'suppliers': self.get_data_for_manual_reconciliation('partner', partner_ids, 'payable'),
            'accounts': self.get_data_for_manual_reconciliation('account', account_ids),
        }
    @api.model
    def get_data_for_manual_reconciliation(self, res_type, res_ids=None, account_type=None):