Has a bug: WebSocket client disconnects are not detected.
rfbSendFramebufferUpdate is doing a MSG_PEEK recv to determine if
enough data is available which prevents a disconnect from being
detected.

Otherwise it's working pretty well.

[jes: moved added struct members to the end for binary compatibility with
previous LibVNCServer versions, removed an unused variable]
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>