AR connection close

looking at 1d9aeefc08fc72f3291ad14aac91fda5434fb519 I must have confused you guys ... sorry 'bout that

I sure did not meant to remove connections from the pool (unless you have reasons for that), I've fixed it at one more place. 

now, regarding `StreamingResultSet` I thought it's going to be returned directly as a Rack body, so far (have not checked in detail) it seems to me that closing the connection there might introduce issues instead of solving any.