BaseAttachmentContentExtractor missing or moved in 2.3-dr2

The current instructions for a attachment extractor suggest to extend bucket.search.lucene.extractor.BaseAttachmentContentExtractor.

http://confluence.atlassian.com/x/TNYB

I can't see this class in the atlassian-bucket-2006.06.15.jar.

The archive extractor plugin fails in 2.3-dr2 because this class cannot be found:
There was a problem loading the descriptor for module 'extractor' in plugin 'Archive Extractor'. Error retrieving dependency of class: com.atlassian.confluence.plugins.extractors.ArchiveContentExtractor. Missing class: bucket/search/lucene/extractor/BaseAttachmentContentExtractor