* macports: Replace update_ports with selfupdate
- Macports discourages use of `port sync` and recommends using `port
selfupdate` instead.
- Keep `update_cache` and `update_ports` as aliases.
- No longer require the `name` parameter so that `selfupdate` can be
used in a task by itself.
* macports: Add upgrade parameter
- New upgrade parameter which can be used to upgrade all outdated ports.
* Add changelog fragment
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