For some obscure reason _validate used to immediately
rollback the current transaction as soon as a constraint
failed anywhere. This is completely incorrect and
violates the transaction abstraction: the responsibility
of creating and closing transactions belongs to the
RPC dispatch layer, or whatever takes its place (e.g. the
test setup/teardown for tests). Rolling back or committing
in the middle of a transaction precludes special
error treatment and can have very bad side effects.
bzr revid: odo@openerp.com-20121029180742-2gw08kobdh7w5njc
485e437440