Recommended BerkleyDB version for use with OpenLDAP 2.1.25 (and later)

[Michael Donnelly <donnelly@sendmail.com>]

The installation notes don't make it entirely clear, the README stops at 
saying "BDB backend requires Sleepycat Berkeley DB 4.1".

What is the *recommended* version of Berkeley DB to use when building 
OpenLDAP 2.1.25 or 2.1.26 (with patches)?
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