VRT: make relativeToVRT=1 work with NITF_IM:, NETCDF:, HDF5:, RASTERLITE:

git-svn-id: https://svn.osgeo.org/gdal/trunk@27080 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx