If you pass an index that has a segment > maxMergeDocs or maxMergeSize
to addIndexesNoOptimize, it throws an IllegalArgumentException.
But this check isn't reasonable because segment merging can easily
produce segments over these sizes since those limits apply to each
segment being merged, not to the final size of the segment produced.
So if you set maxMergeDocs to X, build up and index, then try to add
that index to another index that also has maxMergeDocs X, you can
easily hit the exception.
I think it's being too pedantic; I plan to just remove the checks for