Support block association extensions in modules (from Trac #6450)

this is copied over from Trac, where it was never applied:

http://dev.rubyonrails.org/ticke...

The following association fails when a block extension is specified:

module Widdle
  class Foo
    has_many :bars do
      def do_something
      end
    end
  end
end

In this case, create_extension_module generates the name Widdle::FooBarsAssociation and attempts to set that constant name in Object. However, it should rather generate the name FooBarsAssociation and set that constant name in the module Widdle. This patch addresses the issue.

Also, this bug creates a concrete problem with acts_as_versioned and Rails 2.1.1. I have rebased the patch to edge (it actually did not need any changes) and reran the tests.