Turn on logging 30% of the time.
Copy keys into the in-memory log for transactions: ordinary operations no longer point at any on-page structures apart from WT_UPDATEs.
Leak fix: destroy a condition variable used by the log manager.
If we skip any updates on a page, they must be restored after a save/restore.  If the oldest transaction ID moves while we are reconciling a page, we could skip an update but then decide that all updates on a page are stable.  When the page is restored, the skipped update is lost.

refs #969