XBufferedThreadedStream class buffers data in a new thread,
which will be available to be read from parent thread.

Change-Id: I62d367fa1dec23da39aba24b5c765b57707956bb
Reviewed-on: https://gerrit.libreoffice.org/38135Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>