Make TwentyTen footer.php credits line filterable (for child themes)

[nathanrice]

Assuming we want people to build child themes based on TwentyTen, it makes sense to allow designers/developers to filter the credits line rather than replace the entire footer.php file.

This patch will allow the line to be filtered.

[westi]

If a child theme wants to put its own credits in then I think it would do better to over load footer.php or we add a action for additional credits to be added.

Filtering the output of all those translations / sprintf functions for them to be overloaded by a child theme on every page load is just a waste of cycles.

[jorbin]

They are already filterable by using the i18n functions. see ​http://blog.ftwr.co.uk/archives/2010/01/02/mangling-strings-for-fun-and-profit/

[nathanrice]

Use an action instead of a filter

[nathanrice]

Good point. I just re-uploaded and added an action in front of the WP credit text, instead of filtering the entire credits line.

[nacin]

(In [14433]) Twenty Ten spacing and string cleanups. props zeo, markmcwilliams. see #13198. Add a twentyten_credits filter, props nathanrice, fixes #12804. Also clean up the generator/credits string.