Periodically close session and connection dhandles that are no longer
used. (#586)
Code movement from review comments.
The change in 3d2b80f5f6 broke the test suite, make the fix.
Merge branch 'develop' into dhandle
Merge pull request #620 from wiredtiger/dhandle

Periodically close session and connection dhandles that are no longer
Merge branch 'develop' into prefix-compression-min