Installing http_authentication plugin leaves out lib directory

When I install the http_authentication plugin thusly:

$ script/plugin -v install http://svn.rubyonrails.org/rails/plugins/http_authentication/
Plugins will be installed using http
fetching from 'http://svn.rubyonrails.org/rails/plugins/
http_authentication/'
+ ./http_authentication/README
+ ./http_authentication/Rakefile
+ ./http_authentication/init.rb
+ ./http_authentication/test/basic_test.rb
+ ./http_authentication/test/digest_test.rb

... as you can see, it leaves out ./http_authentication/lib.
Consequently, this no workie.

Interestingly, the following does provide the lib directory:

$ script/plugin install -x http://svn.rubyonrails.org/rails/plugins/http_authentication/

What's the deal?

Thanks.

Michael