Changes:

• only one client port for each provider:
  • databases/mysql-client
  • databases/mariadb-client
• servers install to ${LOCALBASE}/${provider}${version}
• new default version MYSQL_CLIENT_DEFAULT=mysql|mariadb
• mysql.mk only adds run or build depends on ${MYSQL_CLIENT_DEFAULT}

The greatest benefit of this is, that one can have multiple
mysql/mariadb servers installed at once; which makes migrations
to never server versions finally easier.

The respective client ports should be kept at the version of the latest
provided server package. So if there is a databases/mysql82-server port
in the future, databases/mysql-client should be updated to use that one.

Note: the clients are backwards compatible.

This is following the idea proposed back in 2015 [1] for the postgresql ports.
I plan to implement the same "one client-port, multiple-server ports in prefix"
for them as well after this change is finished.

[1] https://lists.freebsd.org/pipermail/freebsd-ports/2015-July/099842.html

TODO:

1. Test the change ;-) -- ideally by someone who has actually some DBs
2. Remove IGNORE_WITH_MYSQL -- as the packages no longer pull in a server this becomse meaning less. You just installl the package and a compatible server backend.
3. Cleanup dependencies -- there are ports that have specific server options. They should be removed, as servers should be chosen by the administrators.
4. Double-check the RC scripts that they make sense this way.
5. Fix up plists in the server ports (they stage, but maybe could need some love :D) [...] n) Bump revision of all ports with USES=mysql