[MacPorts] #47290: digikam: Add variant for external mysql database; rename variant for internal mysql database; update mysql dependency

[MacPorts]

#47290: digikam: Add variant for external mysql database; rename variant for
internal mysql database; update mysql dependency
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  Reporter:  sk-public@…  |      Owner:  macports-tickets@…
      Type:  defect       |     Status:  new
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:  2.3.3
Resolution:               |   Keywords:
      Port:  digikam      |
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Comment (by ryandesign@…):

 What does it mean, "internal" and "external" MySQL databases?

 Changing the dependency to "`path:bin/mysql_config:mysql56`" is not
 correct because the mysql56 port does not provide the file
 /opt/local/bin/mysql_config. Instead, you would just write
 "`port:mysql56`". But typically there should be variants allowing the user
 to choose which MySQL implementation they want: mysql55, mysql56, mariadb,
 mariadb-10.0, mariadb-10.1 or percona. The naming of these variants,
 especially the mariadb ones, has not yet been standardized. In each
 variant you will need to inform the configuration system somehow where
 that MySQL is located.

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Ticket URL: <https://trac.macports.org/ticket/47290#comment:1>
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