I'm trying to upgrade Ubuntu packages and see some strange names flying across the screen.
This package naming convention is throwing me off just a bit :-)
What is 5.1.30really5.0.75?
It looks like jaunty and karmic were using these to transition people from 5.0 to 5.1. According to Ubuntu's changelogs these packages were mostly backports from Debian unstable, since Debian stable is still using 5.0. There's a lot of stuff in their changelogs and a lot of noise on various packages' bugtrackers from around that time about the change from libmysqlclient15 -> libmysqlclient16, which looks like it didn't get completed until lucid.