Provide the "D" in ACID, so that the effects of a transaction become durable on commit rather than on checkpoint.

Current status:

• [x] log manager
• [x] recovery of basic operations
• [x] two-pass recovery (metadata, then ordinary files)
• [x] assign file IDs, cache cursors during recovery
• [x] support truncate
• [ ] fold "meta tracking" code into ordinary recovery
• [ ] test recovery of "DML" operations (create, drop, rename) – via test/fops?