[CMake] Telling CMake to use zlibConfig.cmake instead of the Findzlib.cmake

[Bill Hoffman]

Doug Henry wrote:
> I have not seen a repo for cmake files like that, but I have a feeling 
> there are cmake build files for zlib, png, etc in the VTK source 
> (vtk.org <http://vtk.org>).
Another thing for people to do, is to request that the maintainers of 
zlib, png, etc, add CMakeLists.txt files to the projects sources.
It will help to promote CMake, and we have the files for many of these 
packages, so the maintainers will not have to do much work.


-Bill