title: "no such file to load -- pg" when trying rake db:create
body: <p>The symptom of my problem is pretty simple:</p>
  
  <pre><code>$ rake db:create
  (in /home/jason/projects/blog)
  rake aborted!
  no such file to load -- pg
  
  (See full trace by running task with --trace)
  </code></pre>
  
  <p>I've already successfully run <code>bundle install</code> and <code>gem install pg</code>, so I don't know what else I might need to do.</p>
  
  <p>Here's my `config/database.yml if it helps:</p>
  
  <pre><code># SQLite version 3.x
  #   gem install sqlite3-ruby (not necessary on OS X Leopard)
  development:
    adapter: postgresql
    encoding: unicode
    database: blog_development
    pool: 5
    username: blog
    password: foo
  
  # Warning: The database defined as "test" will be erased and
  # re-generated from your development database when you run "rake".
  # Do not set this db to the same as development or production.
  test:
    adapter: postgresql
    encoding: unicode
    database: blog_development
    pool: 5
    username: blog
    password: foo
  
  production:
    adapter: sqlite3
    database: db/production.sqlite3
    pool: 5
    timeout: 5000
  </code></pre>