[ITK] How to avoid NIFTI header files from being installed?

[Niels Dekker]

With ITK 4.12.2, ITKNIFTI has moved from the DEPENDS section to the 
PRIVATE_DEPENDS section of NIFTI IO module, and I think that's a good 
thing:

   
https://github.com/Kitware/ITK/blob/v4.12.2/Modules/IO/NIFTI/itk-module.cmake
   
https://github.com/Kitware/ITK/commit/940f68ec18b15e500cc22d8ddb1dbae34b66cb2f#diff-72c0401735029f07ee8f10df8269b871

The internal interface between ITK and NIFTI should not be leaked to ITK 
user applications, so that's just fine.

However, when doing an INSTALL, nifti1.h and nifti1_io.h (as well as 
itk_nifti_mangle.h) are still copied to the user's install directory:

  -- Installing: <my-install-dir>/include/ITK-4.12/itk_nifti_mangle.h
  -- Installing: <my-install-dir>/include/ITK-4.12/nifti1.h
  -- Installing: <my-install-dir>/include/ITK-4.12/nifti1_io.h

Is this really necessary?  If not, how could this possibly be fixed?

Kind regards, Niels
-- 
Niels Dekker
Scientific programmer
LKEB, Leiden University Medical Center, Netherlands