Fix warnings appearing in the logs when importing a XAR

2010-01-27 22:03:06,355 [http://localhost:8080/xwiki/bin/register/XWiki/Register] INFO  .AbstractXWikiMigrationManager  - No storage migration required since current version is [15429] 
2010-01-27 22:22:34,590 [http://localhost:8080/xwiki/bin/import/XWiki/Import?editor=globaladmin&section=Import] WARN  rnal.DefaultObservationManager  - The [com.xpn.xwiki.plugin.lucene.IndexUpdater] listener has
overwritten a previously registered listener [com.xpn.xwiki.plugin.lucene.IndexUpdater] since they both are registered under the same id [lucene]. In the future consider removing a Listener first if you really want to register 
it again. 
2010-01-27 22:22:34,599 [http://localhost:8080/xwiki/bin/import/XWiki/Import?editor=globaladmin&section=Import] WARN  rnal.DefaultObservationManager  - The [com.xpn.xwiki.plugin.rightsmanager.RightsManager]
listener has overwritten a previously registered listener [com.xpn.xwiki.plugin.rightsmanager.RightsManager] since they both are registered under the same id [rightsmanager]. In the future consider removing a Listener 
first if you really want to register it again. 
2010-01-27 22:22:34,915 [http://localhost:8080/xwiki/bin/import/XWiki/Import?editor=globaladmin&section=Import] WARN  rnal.DefaultObservationManager  - The 
[com.xpn.xwiki.plugin.activitystream.impl.ActivityStreamImpl] listener has overwritten a previously registered listener [com.xpn.xwiki.plugin.activitystream.impl.ActivityStreamImpl] since they both are registered under the 
same id [activitystream]. In the future consider removing a Listener first if you really want to register it again. 
2010-01-27 22:22:34,946 [http://localhost:8080/xwiki/bin/import/XWiki/Import?editor=globaladmin&section=Import] WARN  rnal.DefaultObservationManager  - The [com.xpn.xwiki.plugin.watchlist.WatchListStore] listener 
has overwritten a previously registered listener [com.xpn.xwiki.plugin.watchlist.WatchListStore] since they both are registered under the same id [watchliststore]. In the future consider removing a Listener first if you really 
want to register it again. 
2010-01-27 22:22:35,978 [http://localhost:8080/xwiki/bin/import/XWiki/Import?editor=globaladmin&section=Import] INFO  internal.JBossCacheCache        - The node /xwiki should not has been removed 
2010-01-27 22:22:35,979 [http://localhost:8080/xwiki/bin/import/XWiki/Import?editor=globaladmin&section=Import] INFO  internal.JBossCacheCache        - The node /xwiki should not has been removed