Add --ignore-database option to mysqldump

mysqldump has a --ignore-table option to exclude individual tables from a dump, it does not have a similar --ignore-database option to ignore a specific database in an --all-databases dump though.

So if I'd only want to exclude a specific database, like e.g. the "sys" database, I'd have to list all databases but the one I'd want to exclude with "--databases db1 db2 ..." individually, and modify the list whenever a new database is created.

Having an "all databases but ..." feature would be a more comfortable and less error prone way to solve this.