Crash vulnerability with nojournal after create during checkpoint

WiredTiger was changed in WT-2346 and WT-2426 to allow new tables to be created while a checkpoint is in progress. When logging (aka journal) is enabled, a table create simply flushes its metadata update to the log, making it durable even if there is a crash before the checkpoint completes.

When logging is disabled, the create operation will sync the metadata to disk. It appears that this can cause some / all of the checkpoint's metadata changes durable before the checkpoint has completed, leading to a window where the on-disk data is not consistent in the event of a crash.