wiredtiger/wiredtiger — pull request #1456 by michaelcahill (2014-12-10 00:11:46+00:00)
Title: Allow sweep to reclaim more handles

In particular,

1. close stale trees in cache even if the data handle is cached in multiple sessions;
2. only mark handles "in use" for the purposes of sweeps if a cursor is opened on them -- not just due to periodic operations such as checkpoints or gathering statistics.