Aside from "9. Online abandoned lock removal" in your release
announcement for 4.4.16, I can't find any documentation describing how
abandoned lock detection and cleanup works.

How does abandoned lock detection work?

Do I need to specify anything special when opening the environment?

Is abandoned lock removal also tied to the DB_REGISTER flag?

Is there a way for the application (like a watcher process) to learn
when BerkeleyDB released an abandoned lock ?

You can look at the failchk method:

http://www.sleepycat.com/docs/api_cxx/env_failchk.html

Ron