Tagcloud: urlify to compare with url param

Hey Bastian—
Some explanation first, why I think this is necessary: I combined the tagcloud plugin and the tag field type to create a self-generating submenu of categories in a blog. The posts would be filtered in accordance to a url parameter. So the links in the submenu would be something like this:
```
/blog/c:foo
/blog/c:bar
```
As it is a catalan/spanish site, I had some issues with accents— both being passed by url, and later correctly recognizing tags as active.
I could fix this by passing a urlified string and comparing that to an urlified version of the tags.