This is a change in search result behavior in that location
information is no longer provided by default with search results.
Although this looks like a wide-ranging change, it's mostly a
mechanical replacement of the explain bool flag with a new
search.SearcherOptions struct, which holds both the Explain bool flag
and the IncludeTermVectors bool flag.
From diagnosing a recent issue where the termSearchersFinished stats
were incorrectly tracked, I ended up scouring the Close() / cleanup
codepaths.
This change takes more care in Close()'ing child searchers, especially
in error situations. This can be important to allow underlying
kvstore's to release resources.
