7.0: work needed in currency_rate_update

[Alexandre Fayolle - camptocamp]

On MP https://code.launchpad.net/~camptocamp/account-financial-tools/7.0-cleaning-currency_rate_update-20130319/+merge/154043, Alexis de Lattre commented:

By the way, if you have some time and you are working on cleaning-up this module, there is a lot of code to trash in company.py. In particular, the field "multi_company_currency_enable" on res.company should be removed (it was usefull in v5 when res.currency didn't have a company_id field, but this field is now standard - since v6.0 I think). All the related code should be removed too, without breaking anything.

I started to code on this a while ago, but I had some difficulties to understand the logic of the function on_change_auto_currency_up() which reads the field multi_company_currency_enable, so I didn't finish the work.

But it may be out-of-scope for this MP...