COMP: Use internally consistent zlib
The zlib libraries are used by many differnt packages includeing ITKv4, LibArchive, VTK, python, and teem.
This patchset builds a single version of zlib that is mangled with a slicer namespace, and uses that one library for all zlib operation throught the "USE_SYSTEM_ZLIB" options.
The mangling for vtk_zlib is disabled for teem because it is not needed when using the External_zlib build.