After you install 'will_paginate', you may see the strange error like:
Missing these required gems:
ruby 22.214.171.124 at /usr/bin/ruby1.8
rubygems 1.3.5 at /home/ci/.gem/ruby/1.8, /usr/lib/ruby/gems/1.8
Run `rake gems:install` to install the missing gems.
And, even though you try to install 'mislav-will_paginate', it does not allow to install it.
Then, it is because you miss a source so that you need to add the following source as follows:
gem sources -a http://gems.github.com
gem install mislav-will_paginate