support for streams2 in `SubDB::createReadStream`

ReadStreams with values where not useable together with pull-stream in nodejs v0.10.16 because `s.on('data', function (d) {})` forces the stream2 into flowing mode but stream-to-pull-stream still detects it as a stream2.

Under nodejs v0.10.16 the tests where failing before this patch. Now they pass.