Confirm matching taxonomy in wp_list_categories()

[nacin]

In wp_list_categories(), we detect the current category using the queried object. But, we don't check if the taxonomy of the queried object matches what we're displaying with wp_list_categories(). Clearly, the current category for purposes of listing categories needs to be the same taxonomy.

A get_term() call in Walker_Category will end up failing and we'll end up with warnings for trying to access non-existent properties. I traced that up the stack to here.

Also adding in is_tag() to the current term check because there's no reason why someone can't use wp_list_categories() for any taxonomy AFAIK.

[nacin]

(In [16250]) Confirm that the queried term object is of the requested taxonomy in wp_list_categories. fixes #15347.