[FIX] payment_buckaroo: dynamic lang & test params

test flag is set according to acquirer environment
lang is set according to partner language
[FIX] payment_buckaroo: api expects iso culture as language param

IT looks like this is the code we use in partner lang, by replacing the '_' (underscore) by '-' (dash)
[FIX] purchase: supplier invoice and purchase order count

Value of purchase_order_count and supplier_invoice_count should be coherant with
the behaviour of the button on partner form: count records for the contact of
the company as well.
Fixes #4224
Reintroduce fname kwarg in configmanager

In [f04f409], the configmanager's __init__ lost its fname kwarg, which
allows to pass the name of the config file to read (or write).
Without it the only way to programmatically specify this file name is to
use the OPENERP_SERVER environment variable, which may be unpractical and/or
subject to renaming.

External tools (such as the buildout recipe) may need to pass this file in a
clean way.