account_invoice_merge/wizard/invoice_merge_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <record id="view_invoice_merge" model="ir.ui.view">
            <field name="name">Merger Partner Invoice</field>
            <field name="model">invoice.merge</field>
            <field name="arch" type="xml">
                <form string="Merge Partner Invoice" version="7.0">
                    <group>
                        <separator
                            string="Are you sure you want to merge these invoices ?"
                            colspan="4" />
                        <p>
Please note that:<br/><br/>
Invoices will only be merged if:<br/>
* Invoices are in draft<br/>
* Invoices belong to the same partner<br/>
* Invoices are have same company, partner, address, currency, journal, salesman, account, type<br/><br/>
Lines will only be merged if:<br/>
* Invoice lines are exactly the same except for the product,quantity and unit<br/>
                            </p>
                    </group>
                    <group name="options">
                        <field name="keep_references"/>
                        <field name="date_invoice"/>
                    </group>
                    <footer>
                        <button name="merge_invoices" string="Merge Invoices"
                            type="object" class="oe_highlight" />
                        or
                        <button string="Cancel" class="oe_link"
                            special="cancel" />
                    </footer>
                </form>
            </field>
        </record>

        <act_window name="Merge Partner Invoice" res_model="invoice.merge"
            src_model="account.invoice" view_mode="form" target="new"
            multi="True" key2="client_action_multi" id="action_view_invoice_merge" />

    </data>
</openerp>