Fix a long-standing bug where a page could be marked clean (and evicted) when it contained uncommitted changes.

refs #835, #818(?), #581
Rollback transactions in connection close as a separate pass before closing all of the sessions.

refs #835
Merge pull request #878 from wiredtiger/evicting-uncommitted

Fix a long-standing bug where a page could be marked clean (and evicted)...
Merge branch 'develop' into new-split