bdb 4.2->4.3 upgrade

[Florian Weimer]

* Max Bowsher:

>> You should perform a checkpoint before the recover, but otherwise,
>> it's fine.
>
> Do you have a reference for this?

Recovery replays logs from the last checkpoint (after nuking the
cache, which is potentially dirty).  Recovery is basically a no-op
when you minimize the number of logs.  In short, it's just an
optimization.

> http://www.sleepycat.com/docs/ref/upgrade/process.html
> did not mention a checkpoint at all in the 4.3 era.
> Now, it is stating that you must checkpoint as the first thing you do
> with the _new_ bdb version.

These instructions cannot work because there is no database
environment when db_checkpoint is invoked, and db_checkpoint cannot
create one on its own.

> 'svnlook youngest' does the job quite well.

Ah, good to know.