tag_counts broken in Rails 3

[pdeffendol]

Calling #tag_counts causes the creation of invalid SQL when using this with Rails 3. It turns out that the #scope method on ActiveRecord::Base no longer does the same thing as in Rails 2.3. (It was renamed from #named_scope for Rails 3.)

I made a temporary fix on my fork at http://github.com/fragility/acts_as_taggable_on_steroids/commit/3994188312ba7404f31aa70a997b2a8487868aa5 but it's kind of a cop-out.