mrp_byproduct does not accept or preserve context on action_confirm

The mrp_byproduct module overrides the action_confirm method on the mrp.production object. However, the overriding method has a signature of

  def action_confirm(self, cr, uid, ids):

while the original method defined in the mrp module has a signature of

  def action_confirm(self, cr, uid, ids, context=None):

This causes issues when further extending the mrp.production object while mrp_byproduct is installed. The attached patch adds the context variable to both the function definition and the super call inside of action_confirm().