[ZODB-Dev] Savepoints are invalidated once they are used

[Tim Peters]

[Tim Peters]
...
> OTOH, the transaction.Savepoint.rollback() implementation is a bit
> schizophrenic:  it invalidates self, but leaves it in the transaction's
> stack (for savepoints "after" self, it both invalidates them and removes
> them from the transaction's stack).

Oops!  Not true.  It does remove self from the stack.