Aware user (who *does* know all the files whose names

Aware user (who *does* know all the files whose names
are in InternalFileNameList are 'coherent', that is to say :
- exist
- may be open,
- are gdcm-readable
- have the same sizes
- have the same 'pixel' type
- are single frame
- have the same color convention
- anything else ?
is now allowed to ask for a 'light' checking (actualy : initialization, from the
first file characteristics), using vtkGdcmReader::SetCheckFileCoherenceLight()