Many2Many are also not sortable

The Many2Many are like One2Many not sortable by default.

assigned to @ced

added trytond type::crash + 1 deleted label

Here is review15821002

New changeset 5feeca6a3983 by C?dric Krier in branch 'default':
Many2Many are not sortable
http://hg.tryton.org/trytond/rev/5feeca6a3983

added 1 deleted label and removed 1 deleted label

closed

New changeset dcd40db1361c by C?dric Krier in branch '3.8':
Many2Many are not sortable
http://hg.tryton.org/trytond/rev/dcd40db1361c

New changeset a685c12ddb81 by C?dric Krier in branch '3.6':
Many2Many are not sortable
http://hg.tryton.org/trytond/rev/a685c12ddb81

New changeset 81ded07ec18c by C?dric Krier in branch '3.4':
Many2Many are not sortable
http://hg.tryton.org/trytond/rev/81ded07ec18c

New changeset e9fe1620d2e0 by C?dric Krier in branch '3.2':
Many2Many are not sortable
http://hg.tryton.org/trytond/rev/e9fe1620d2e0

New changeset 41e0c833f2fd by C?dric Krier in branch '3.0':
Many2Many are not sortable
http://hg.tryton.org/trytond/rev/41e0c833f2fd