Missing mult_add function in base_vat module

[Jordi Esteve (www.zikzakmedia.com)]

The mult_add function used to verify some vat numbers is missing in base_vat module (Austria, Spain, Italy and Sweden VAT verification use it).

The following function must be add at begining of base_vat/partner.py (see http://hg.tryton.org/vatnumber/rev/d543918be65f):

def mult_add(i, j):
    '''
    Sum each digits of the multiplication of i and j.
    '''
    mult = i * j
    res = 0
    for i in range(len(str(mult))):
        res += int(str(mult)[i])
    return res

[Christophe Simonis (OpenERP) (kangol)]

fixed.
But smarter method has been added :D