* use stream directly in chronosstream
for now, chronos.AsyncStream is not used to provide any features on top
of chronos.Stream, so in order to simplify the code, chronosstream can
be used directly.
In particular, the exception handling is broken in the current
chronosstream - opening and closing the stream is simplified this way as
well.
A future implementation that actually takes advantage of the AsyncStream
features would wrap AsyncStream instead as a separate lpstream
implementation, leaving this one as-is.
* work around chronos exception type issue
ccd019b328