cmake/modules/FindVIGRA.cmake: Try to get VIGRA_ROOT from the path.
cmake/modules/FindVIGRA.cmake: Switch VIGRA_INCLUDE_DIR search order.
cmake/modules/FindVIGRA.cmake: Use local variable VIGRA_ROOT instead of the environment one.
cmake/modules/FindVIGRA.cmake: Export VIGRA_ROOT.
cmake/modules/FindVIGRA.cmake: Rename VIGRA_VIGRANUMPYCORE_LIBRARY_DIR to the more general VIGRANUMPY_SITEPACKAGE_DIR.
CMakeLists.txt: Set VIGRA_ROOT instead of VIGRA_INCLUDE_DIR.
CMakeLists.txt: Remove space.
CMakeLists.txt: Don't set PYTHON_EXECUTABLE as we can find it.
cmake/modules/FindVIGRA.cmake: Fix spacing.
cmake/modules/FindVIGRA.cmake: Document VIGRA_ROOT being exported.
CMakeLists.txt: Keep PYTHON_EXECUTABLE setting in comment if needed.