Make the tag search case insensitive

Today, when specifying the tag for the searched pages, the tag resolution is case sensitive.

However, the other tag usages by the standard tag application are case insensitive:

• in the tagcloud the tags are case-insensitive (the tags that differ only by case are counted and displayed only once)
• when listing the pages in the tag page (after clicking the tag in the tag cloud), all pages are displayed, regardless of the case of the tag on the page.

To align the behaviour of this macro with the tag module, this macro should also list pages regardless of the case of the tag used on the page.