Fix a bug where rolling back the first transaction to update an LSM tree could leave the metadata inconsistent.

refs #976
Add a -F option to thread, to create a separate file for every thread.
With this option, the command line combination "-FS -R 0 -W 10" will
trigger the checkpoint problem where closing a file fails because there
is an update for the file we can't write.

Reference #844, #957.
Update.