FL-1499: Fixed error message if mysql is not configured in /etc/init.d/m...

Running `rc-service mysql start` when mysql is not configured tells:

You don't appear to have the mysql database installed yet.
Please run /usr/bin/mysql_install_db to have this done...

The later only exist as a man page :

$ whereis mysql_install_db
mysql_install_db: /usr/share/man/man1/mysql_install_db.1.bz2

The actual command to issue is `emerge --config dev-db/mysql`.


See https://bugs.funtoo.org/browse/FL-1499