more tests
Streams2 (bug + tests)

Fixed a bug with writable streams and drain state. Previously
the drain counter would become negative and backpressure
would no longer be respected or pipes would break.

Fixed a bug with unpipe where the pipe would break because
the flowing state was not reset to false.

Fixed a bug with sync cb(null, null) in _read which would
forget to end the readable stream

Added more test cases for object streams