Ideally, the CopyToQueryStream would take care o piping, unpiping and
resuming the connection with the DB.
For some reason it does not always work when trying that from the
_transform callback.
Since there's no better callback (at least in node6), this patch is
required to make sure that such connection can be returned to the pool
and reused by some other query.
d5a7f6d2d6