Major Description
spinoff from LUCENE-4371:
Currently NIOFSDirectory.NIOFSIndexInput extends SimpleFSDirectory.SimpleFSIndexInput, but this isn't an is-a relationship at all.
Additionally SimpleFSDirectory has a funky Descriptor class that extends RandomAccessFile that is useless:
/**
* Extension of RandomAccessFile that tracks if the file is
* open.
*/
...
// remember if the file is open, so that we don't try to close it
// more than once
RandomAccessFile is closeable, this is not necessary and I don't think we should be subclassing it.