Copy header files (the ones that will be installed) to ${CMAKE_BINARY_DIR} before building any ROOT library. Copy also tutorials, icons, etc,... so that we do not need to enable -Dtesting=ON to execute any program of macro.
Re-enable the creation of hsimple.root.
Install Xrootd libraries into ${ROOTSYS}/lib when using builtin_xrootd option.
Do not trigger the creation of hsimple.root, which may create clashes when running in parallel.