Ambiguous column reference error compute_quantities_query with custom grouping
Calling method Move.compute_quantities_query() with custom grouping gives a backend error of ambiguous column reference.
Can be reproduced with grouping=("product", "effective_date")
Indeed the error is here [1][2][3] due to columns can be repeated. Should be managed with set().
[1] http://hg.tryton.org/modules/stock/file/default/move.py#l1028
[2] http://hg.tryton.org/modules/stock/file/default/move.py#l1013
[3] http://hg.tryton.org/modules/stock/file/default/move.py#l1000