Updated to build against xorg-x11-server 1.16.0.

For #25.

I wasn't able to make cmake happy when testing this so you might want to check it compiles OK.
```
vncExtInit.cc: At global scope:
vncExtInit.cc:79:22: error: conflicting declaration 'const char* display'
../../include/opaque.h:52:24: error: 'display' has a previous declaration as 'char* display'
```