fixup! Support reading uncompressed streams with compressed_stream.
fixup! Simplify can_read().
Add position test 6.
Redo seek(0, end).
Get rid of m_lastItem.
Change m_position to two fields m_readOffset and m_offset.
Make initialization of all fields explicit in stream_base ctor.
Add comment about non-trivial dtor order.
Change compressed_stream_base field order.

ownedTempFile should be freed *after* stream accessor has been
destructed.

m_buffers should be destructed *after* our m_buffer has been freed.