Merge from 2.7 branch:

- Simple parameterization of BUCKET_CLASS for testing/debugging purposes.
  BUCKET_CLASS can be set to something like "dict" in order to isolate
  future problems potentially caused by OOBTrees (not that there seem
  to be any, but it's nice to be able to confirm).
                                                                                
- Log at INFO level in TLOG instead of BLATHER.
                                                                                
- Fix "off by one" error in _getCurrentSlices and explain.
                                                                                
- Add various DEBUG and TLOG statements for testing/debugging purposes.
                                                                                
- Arrange to compare against "default" instead of "_marker" in .get.
                                                                                
- Use random.uniform instead of random.choice to decide how to sleep.
                                                                                
- Use "_wrap" instead of directly calling __of__ for consistency.