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
""" This function iterates recursively on the recordset given as parameter as long as it
            can find a debit and a credit to reconcile together. It returns the recordset of the
            account move lines that were not reconciled during the process.
        """
        if not self.ids:
            return self
        sm_debit_move, sm_credit_move = self._get_pair_to_reconcile()
        
        if not sm_credit_move or not sm_debit_move:
            return self
        field = self[0].account_id.currency_id and 'amount_residual_currency' or 'amount_residual'
        if not sm_debit_move.debit and not sm_debit_move.credit:
            
            field = 'amount_residual_currency'
        if self[0].currency_id and all([x.currency_id == self[0].currency_id for x in self]):
            
            field = 'amount_residual_currency'
        if self._context.get('skip_full_reconcile_check') == 'amount_currency_excluded':
            field = 'amount_residual'
        elif self._context.get('skip_full_reconcile_check') == 'amount_currency_only':
            field = 'amount_residual_currency'