Revision 1141542

  SOLR-2193, SOLR-2565: The default Solr update handler has been improved so
  that it uses fewer locks, keeps the IndexWriter open rather than closing it
  on each commit (ie commits no longer wait for background merges to complete), 
  works with SolrCore to provide faster 'soft' commits, and has an improved API 
  that requires less instanceof special casing. 

  You may now specify a 'soft' commit when committing. This will
  use Lucene's NRT feature to avoid guaranteeing documents are on stable storage in exchange
  for faster reopen times. There is also a new 'soft' autocommit tracker that can be
  configured.

 SolrCores now properly share IndexWriters across SolrCore reloads.