title: Luke says my Lucene index directory is Invalid
body: <p>I'm trying to learn about Lucene, and hope to use Luke to investigate it.  I tried building an index with the IndexFiles demo in Lucene 4.3, then tried viewing the index with the latest version of Luke, and I'm getting the message:</p>
  
  <pre><code>Invalid directory at the location, check console for more information. Last exception:
  org.apache.lucene.index.IndexFormatTooNewException: Format version is not supported (resource: ChecksumIndexInput(MMapIndexInput(path="/home/lavin/sep20.index/segments_2"))): 1 (needs to be between 0 and 0)
  </code></pre>
  
  <p>Any ideas what's wrong and how to fix?   Is my version of Lucene too new for Luke to decipher?   Is there a way I can tell Lucene to write an older version of the index?   Thanks in advance, 
  -- Mark</p>