[tryton-dev] trytond: Use one getter for all amounts in Sale, Purchase and Invoice (issue 897002)

[cedric . krier]

Reviewers: ,



Please review this at http://codereview.tryton.org/897002/

Affected files:
  M trytond/modules/account_invoice/invoice.py
  M trytond/modules/purchase/purchase.py
  M trytond/modules/sale/sale.py