Uprade lucene to 2.3

[Yongjun Rong]

Hi,
  It seems the latest lucene 2.3 has some improvement on performance.
I'm just wondering if it is ok for us to easily upgrade the solr's
lucene from 2.1 to 2.3. Is any special thing we need to know except just
replace the lucene jars in the lib directory.
  Thank you very much.
  Yongjun Rong