Bugfix. Handling openssl quirkiness.  We need to use SSL_MODE_RELEASE_BUFFERS in addition to
SSL_MODE_ENABLE_PARTIAL_WRITE  if we want SSL_write to
behave like write (our implicit assumption). Otherwise, SSL_write will
simply fail on retry with different buffer address (but same contents).
Just to be safe, we also just pass the exact same contents or
the exact remainder of previous SSL_write call  on retry.