Implement CMake Policy CMP0023 Use PUBLIC & PRIVATE to set link library interface.

Prior to this patch CMake 2.8.12 would report a warning about what the link
library interface was going to be.
src/QGlib/wrap.cpp Include the name of the GType that wasn't registered.

The assert in ::wrap reported that a type wasn't registered. I thought it
would be useful to know what that type was.