title: rake db:migrate doesn't detect new migration?
body: <p>Experienced with Rails / ActiveRecord 2.1.1</p>
  
  <ul>
  <li>You create a first version with (for example) ruby script\generate scaffold product title:string description:text image_url:string</li>
  <li>This create (for example) a migration file called 20080910122415_create_products.rb</li>
  <li>You apply the migration with rake db:migrate</li>
  <li>Now, you add a field to the product table with ruby script\generate migration add_price_to_product price:decimal</li>
  <li>This create a migration file called 20080910125745_add_price_to_product.rb</li>
  <li>If you try to run rake db:migrate, it will actually revert the first migration, not apply the next one! So your product table will get destroyed!</li>
  <li>But if you ran rake alone, it would have told you that one migration was pending</li>
  </ul>
  
  <p>Pls note that applying rake db:migrate (once the table has been destroyed) will apply all migrations in order.</p>
  
  <p>The only workaround I found is to specify the version of the new migration as in: </p>
  
  <pre><code>rake db:migrate version=20080910125745
  </code></pre>
  
  <p>So I'm wondering: is this an expected new behavior?</p>