[development] Drop MySQL 3 support

[Jakub Suchy]

> Does anyone have any decent numbers on MySQL's 4.0's active use?

The main difference between 4.0 and 4.1 is support for database
charsets, which is "mandatory". That's the main reason why many
webhosters from Czech Republic, Slovakia and other countries using
diacritics stick on 4.0. It's just very difficult and time consuming to
convert all databases...

Jakub Suchy