Add 'require thread' to cookbook_uploader to get Queue defined.

Without this change, when I run

    knife cookbook upload MY_RECIPE

for any recipe, I get the error:

    /usr/lib/ruby/gems/1.8/gems/chef-11.6.0/lib/chef/cookbook_uploader.rb:16:in `work_queue': uninitialized constant Chef::CookbookUploader::Queue (NameError)

With this change, the command works fine.