user's $VNC_OPTIONS overridden if VNC is Xtightvnc

Sorry, I didn't expect that both of my pull requests (they were mutually exclusive) would be merged! :sweat_smile: 

This patch fixes a bug where user-specified VNC_OPTIONS would be *overridden* :bomb: if their chroot'ed Linux happens to be using Xtightvnc as the VNC server. :cake: