WAPBL fixes committed to NetBSD-current

Andrew Doran has committed some fixes which address a number of problems with the logging feature of the fast file system. Logging provides for very fast updates of file system control data, and removes the need to check file systems after a system outage. The full details can be found in Andrew's commit message.

Fixing these aspects of logging is one of the last remaining tasks to be done before the release of 5.0, and so these changes by Andrew bring that event a bit closer - the next stage is for them to be pulled up to the NetBSD-5 branch within the source code repository.

We're very excited to finally ship logging for FFS. For many applications it enables better performance and stronger atomicity guarantees. Additionally, avoiding file system checks is of real importance for servers and embedded systems, where delays in restarting the system cannot be tolerated.