unicode tag dublicates

[yury]

new_tag_names = list.reject { |name| existing_tags.any? { |tag| tag.name.downcase == name.downcase } }

code above work incorrectly with unicode tag names. Names should be downcased with mb_chars.downcase

here is the patch:
http://github.com/yury/acts-as-taggable-on/commit/31385691e989e2b15ddab1d318d673f4cb69ef4e
Can't write test to reproduce problem, because sqlite LIKE is case sensitive with unicode chars.

[eet-nu]

I was unable to pull your commit for some reason, so I've changed the code myself. Thanks for the patch!

[yury]

Cool, thanks