shallow over http or ftp not supported

I am trying to install a custom plugin in my Rails app:

    script/plugin install http://git.eyequeue.net/plugins/mt_capistrano.git

Instead of installing the plugin, I get the following error:

    shallow over http or ftp not supported

Any ideas on how to fix this? Is it OK to do a git clone in my vendor/
plugins directory?

Hi - did you have any luck with this?
Now that github supports http cloning (yay!) I am installing rspec via
git, and the 'script/plugin' method isn't working for me either.

I got it working by following the first set of instructions at
http://github.com/dchelimsky/rspec-rails/wikis/home - i.e. doing a
full git clone into vendor/plugins.

But this seems a bit overly complex to me...

- Korny