cmake/modules/FindVIGRA.cmake: Search for configVersion.hxx or config_version.hxx. Later versions of VIGRA use the latter.
cmake/modules/FindVIGRA.cmake: Get the directory of vigranumpycore.
CMakeLists.txt: Add VIGRANUMPY_SITEPACKAGE_DIR to the library path. Drop VIGRA_VIGRANUMPYCORE_LIBRARY_PATH as that variable is no longer used.