[arch-dev-public] adding X2go to extra

FreeNX isn't maintained upstream anymore. X2go is the current project that develops NX-libs v3 and ship a different set of Server+Client that is a full replacement for remote Client-Server access with similar functionality. X2go packages can be installed along FreeNX/OpenNX/NXclient and later we can drop FreeNX packages if they really die. I'm currently building packages locally based on the AUR packages and I'd like to bring them all to extra with needed build dependencies (only man2html so far). If there are no objections I'll push them over the next few days to testing. -Andy