Linux Archive - MySQL upgrade from 5.1 to 5.5

I did an upgrade on my mediawiki box the other day to fix some
security issues. Well, in the mix, mysql-common was upgraded from
mysql-common_5.1.62-1 to mysql-common 5.5.23+dfsg-1. Nothing happened
until last night when we took a power hit due to a storm, and when it
rebooted, I got

May 25 09:49:06 sisko mysqld[31214]: 120525 9:49:06 [ERROR]
/usr/sbin/mysqld: unknown variable 'lc-messages-dir=/usr/share/mysql'
May 25 09:49:06 sisko mysqld_safe[31217]: ended
May 25 09:49:20 sisko /etc/init.d/mysql[31383]: 0 processes alive and
'/usr/bin/mysqladmin --defaults-file=/etc/mysql/debian.cnf ping'
resulted in
May 25 09:49:20 sisko /etc/init.d/mysql[31383]: /usr/bin/mysqladmin:
connect to server at 'localhost' failed
May 25 09:49:20 sisko /etc/init.d/mysql[31383]: error: 'Can't connect
to local MySQL server through socket '/var/run/mysqld/mysqld.sock'
(2)'
May 25 09:49:20 sisko /etc/init.d/mysql[31383]: Check that mysqld is
running and that the socket: '/var/run/mysqld/mysqld.sock' exists!
May 25 09:49:20 sisko /etc/init.d/mysql[31383]:
May 25 09:57:10 sisko mysqld_safe[10065]: started
May 25 09:57:10 sisko mysqld[10068]: 120525 9:57:10 [ERROR]
/usr/sbin/mysqld: unknown variable 'lc-messages-dir=/usr/share/mysql'
May 25 09:57:10 sisko mysqld_safe[10071]: ended

I tried creating mysql.sock, but it just wouldn't start. So I rolled
back to 5.1.62, and it (and mediawiki and redmine) came up just fine.
Is there some kind of prep work I need to do rather than just
springing an unexpected mysql upgrade on a box, or is this bug worthy?
I checked for a similar bug on bugs.d.o, but didn't see anything...

Thoughts?

Thanks,
--b

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