Fix for issue 330 - "Tag list does not handle non-english text correctly"

This should fix issue #330. 

The problem is that PHP5 does handle UTF-8 natively. (ie: strtolower is really only for ASCII text)
In order to support other languages you need to use mb_strtolower. 
( See http://www.php.net/manual/en/function.mb-strtolower.php for more info )

The only downside to using this though is that it is much SLOWER than strtolower. 

If you have Shimmie setup to cache the tag list then it shouldn't be a problem, but I was thinking that perhaps there should be some option in Shimmie's config for supporting UTF-8 for tags or something.

Any thoughts or ideas are welcome.