[FIX] orm: _validate should not immediately rollback
[FIX] orm: _validate should not immediately rollback

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.

akretion/openerp-server,akretion/openerp-server,akretion/openerp-server