Creates a proper {@link XMLInputSource} from a {@link StreamSource}.
if( in.getReader()!=null )
return new XMLInputSource(
in.getPublicId(), in.getSystemId(), in.getSystemId(),
in.getReader(), null );
if( in.getInputStream()!=null )
return new XMLInputSource(
in.getPublicId(), in.getSystemId(), in.getSystemId(),
in.getInputStream(), null );
return new XMLInputSource(
in.getPublicId(), in.getSystemId(), in.getSystemId() );