Give parnent of current page/category a CSS class

[mdawaffe]

Attached gives current_page_parent and current-cat-parent to the parent of the current object in wp_list_pages() and wp_list_categories().

Recommend that dashes be usedin class names and IDs where ever possible: current-page-parent

​http://developer.mozilla.org/en/docs/Underscores_in_class_and_ID_Names

I agree, but we're already using current_page; I went for current_page_parent for the sake of parallelism. It'd be very confusing to people if one were one way and the other were the other.

How about we give the current page both current_page and current-page and give the parent just current-page-parent?

That'll break some plugins, unfortunately, that are filtering wp_list_pages. Of course, it wouldn't be the first time that the CSS classes for pages was changed... I think it changed in 2.0

Should probably pass by reference for get_page() and get_category

Let's stick with the underscore... I don't like them being different and changing them to dashes would break countless themes and plugins.

(In [4576]) Give CSS class to parent of current page/cat. Props mdawaffe. fixes #3253