Support RFB Protocol for Extended Key Events

[RalfLücking]

For thin client use cases, the key symbol based keyboard handling in classical RFB may cause problems,
as a 100%-mapping may not always exist between the client and server keymap, especially consider to support all possible keyboar layouts available in the world.
In addition the indicator led state may get out of sync.

Similar issues exists for VNC connections to virtual machines, so QEMU has defined two RFB extensions to address these isues:

- Extended key events, which transmits a layout independent scancode together with the keysym
- Keyboard indicator led state notifications from the server to the client

These extensions are documented in rfbproto:
https://github.com/rfbproto/rfbproto/bl ... o-encoding
See also: https://www.ibm.com/developerworks/libr ... index.html

They are supported by gtk-vnc and noVNC on the client side, and QEMU on the server side.

We prepared a pull request within the TigerVNC project to enable support for these protocol extensions there too.
The pull-request has been accepted recently and the feature will be supported within the next TigerVNC release.

I like to ask for feedback from the maintainers if such feature would be welcome for Ultra VNC too?
In case "yes" - we would be willing to contribute to prepare such a commit also for Ultra VNC.

Feedback very welcome!

Best regards, Ralf