Affects Version/s: None
Fix Version/s: 4.10.5
Today when you do the first IW.commit to a 3.x index from Lucene 4.x, we go
through a per-segment upgrade process when writing the next segments_N
file, writing .si files for each segment if we didn't already do so.
However, this process can be fooled by a leftover _N_upgraded.si
file, in case the app above Lucene wasn't careful and reused a
directory that had leftover files... I think we can make this more