This means, call in the correct order the user callback with the correct
parameters (in particular the correct paths for file copy operations),
and check also for the callback returned value to know whether or not to
continue the file operations.
This allows using some of the SetupApi.dll functions when SETUPLIB is
used in the (Win32) GUI 1st-stage installer "REACTOS", while using the
custom implemented NT-aware functions in "USETUP".