[FIX] account_anglo_saxon: avoid incorrect conversion while creating invoice...

[FIX] account_anglo_saxon: avoid incorrect conversion while creating invoice in different currency than the one of the company (opw 606408).

Without this patch the generated entries would use incorrect currencies. The expected result from move_line_get are prices in the currency of the invoice.

bzr revid: mat@openerp.com-20140416082915-555nhsvi8l0mmyxi