bdb 4.2->4.3 upgrade

[Florian Weimer]

* Peter Samuelson:

> (2a) Is the part about deleting log files (taken from faq.html)
> necessary, or incidental?

It is dangerous, not necessary (if you run db4.2_recover anyway), and
does not solve the real problem (the log file incompatibility).

> (2b) Is it possible to simplify the steps somewhat by having the
> user delete *all* the log files unconditionally?  It seems to me
> that after a successful db_recover, this should be safe ... true or
> false?

False.  You must never delete active log files (i.e. those not listed
by db_archive -d).

Berkeley DB 4.3 apparently has a bug which causes it to choke on
old-version log files, but running a read-only "svnadmin" instead of
"db4.3_recover" in the instructions I previously listed should work
around this bug.  (Perhaps the bug can be fixed in the 4.3 package.)

Things get more complicated if Berkeley DB 4.2 is removed in the etch
timeframe (so that db4.2_recover and friends are not available), but
that seems unlikely because other Berkeley DB users will face similar
migration problems.