Wrong tax sign in refunds

[mlaitinen]

Taxes 24 %, 14 % and 10 %, both sales & purchase act wrong in refunds. When refunding a customer invoice (or supplier), the tax should be refunded as well. Now what happens is that the tax part is charged again.

Add

<field name="ref_tax_sign">-1</field>
<field name="ref_base_sign">-1</field>

for all of them.