Default mysql package if there isn't any installed is mysql-4.1.7
(databases/mysql4-client)
You can choose a mysql package via MYSQL_VERSION_DEFAULT, it will
accept the following values:
MYSQL_VERSION_DEFAULT=41 # <- mysql-4.1.7
MYSQL_VERSION_DEFAULT=40 # <- mysql-4.0.21
MYSQL_VERSION_DEFAULT=30 # <- mysql-3.5.x
