我正在关注 Lynda Ruby on Rails 3 Essential Training 视频，刚刚创建了一个新的 Rails 应用程序，预配置为使用 MySQL 数据库：
rails new app -d mysql
然后我进入 /app 目录并尝试启动 rails 服务器：
rails s
这是返回的内容：
/usr/local/rvm/gems/ruby-1.9.3-p392/gems/mysql2-0.3.11/lib/mysql2.rb:9:in 'require': dlopen(/usr/local/rvm/gems/ruby-1.9.3-p392/gems/mysql2-0.3.11/lib/mysql2/mysql2.bundle, 9): Library not loaded: libmysqlclient.18.dylib (LoadError)
Referenced from: /usr/local/rvm/gems/ruby-1.9.3-p392/gems/mysql2-0.3.11/lib/mysql2/mysql2.bundle
Reason: image not found - /usr/local/rvm/gems/ruby-1.9.3-p392/gems/mysql2-0.3.11/lib/mysql2/mysql2.bundle
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/mysql2-0.3.11/lib/mysql2.rb:9:in '<top (required)>'
from /usr/local/rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.2.4/lib/bundler/runtime.rb:68:in 'require'
from /usr/local/rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.2.4/lib/bundler/runtime.rb:68:in 'block (2 levels) in require'
from /usr/local/rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.2.4/lib/bundler/runtime.rb:66:in 'each'
from /usr/local/rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.2.4/lib/bundler/runtime.rb:66:in 'block in require'
from /usr/local/rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.2.4/lib/bundler/runtime.rb:55:in 'each'
from /usr/local/rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.2.4/lib/bundler/runtime.rb:55:in 'require'
from /usr/local/rvm/gems/ruby-1.9.3-p392@global/gems/bundler-1.2.4/lib/bundler.rb:128:in 'require'
from /Users/joemeissler/code/lynda/config/application.rb:7:in '<top (required)>'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/railties-3.2.13/lib/rails/commands.rb:53:in 'require'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/railties-3.2.13/lib/rails/commands.rb:53:in 'block in <top (required)>'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/railties-3.2.13/lib/rails/commands.rb:50:in 'tap'
from /usr/local/rvm/gems/ruby-1.9.3-p392/gems/railties-3.2.13/lib/rails/commands.rb:50:in '<top (required)>'
from script/rails:6:in 'require'
from script/rails:6:in '<main>'
知道这可能是什么吗？我已经安装了 MySQL。mysql2 gem 已安装，我在 Mountain Lion 上。谢谢您的帮助。