Do not allow to assign unknonw field on proteus model
Purchase module not depends with sale module and scenario test has salable = True [1]
review39441002
[1] http://hg.tryton.org/modules/purchase/file/tip/tests/scenario_purchase.rst#l171
Purchase module not depends with sale module and scenario test has salable = True [1]
review39441002
[1] http://hg.tryton.org/modules/purchase/file/tip/tests/scenario_purchase.rst#l171