When we first implemented TLS, we assumed in conneciton_handle_write
that a TOR_TLS_WANT_WRITE from flush_buf_tls meant that nothing had
been written. But when we moved our buffers to a ring buffer
implementation back in 0.1.0.5-rc (!), we broke that invariant: it's
possible that some bytes have been written but nothing.
That's bad. It means that if we do a sequence of TLS writes that ends
with a WANTWRITE, we don't notice that we flushed any bytes, and we
don't (I think) decrement buckets.
Fixes bug 7708; bugfix on 0.1.0.5-rc
Nick Mathewson