Restructure Xvnc/libvnc.so code to avoid C++ header hacks

Restructure Xvnc/libvnc.so code to avoid C++ header hacks

The internal Xorg headers are very incompatible with C++ and we've had
to resort to all kinds of hacks in order to include them in our C++
code. This approach isn't really viable long term so restructure things
so that we have a glue layer written in C that bridges the Xorg core
with the RFB classes.