locking corruption from old bogofilter version

[Matthias Andree]

Hi,

I figured db_verify doesn't find all kinds of data base corruption. I
found out the hard way that bogoutil -d spamlist.db went into an
unterminated loop, although db_verify didn't complain.

It'd probably be best if we, after the current 0.9.2 locking code has
proven to work well, tell users to rebuild their data bases. You never
know how much data gets lost by db_dump -r (which can be used to recover
these data bases) or how much junk db_dump -R digs out from what has
never been data.

We might want to change the code to close and reopen the databases after
every 100 messages or so in order not to hold the lock for too long.

Happy filtering,

-- 
Matthias Andree