fix NPE
implement Lucene46FieldInfosWriter()
implement SegmentCommitInfo ctor
ignore Closer is nil
implement SegmentInfoCommit.Files()
relocate StoredFieldVisitor.Status
relocate SegmentCommitInfo into codec/spi
ignore CPD deleteFile error
fix naming
implement Lucene46SegmentInfoWriter
implement FrozenBufferedUpdates.any()
implement SegmentCommitInfo.toString()
implement BufferedUpdatesStream.prune()
implement IW.updatePendingMerges()
implement TMP.findMerges()
implement SegmentCommitInfo.clone()
implement IW.assertFileExists()
implement SegmentInfos.write()
implement IW.closeInternal()
implement DW.assertEventQueueAfterClose()