It seems like a good idea on the face of it, but lowWaterMarks are
actually not useful, and in practice should always be set to zero.
It would be worthwhile for writers if we actually did some kind of
writev() type of thing, but actually this just delays calling write()
and the overhead of doing a bunch of Buffer copies is not worth the
slight benefit of calling write() fewer times.
Implemented a new property for writable file streams that keeps track
of the bytes written (not queued). This helps when you are piping
another stream to a file, and would like to know how big the file is
without having to issue another stat call.
closes#930
Allows for more fine graining, especially finding out about an individual
chunk of data being flushed in a write stream rather than the whole queue.
This commit also fixes a bug causing forceClose to fail on a readStream that
did not finish opening yet.