title: Add-Migration while there are explicit migrations pending
body: <p>So I have a basic problem trying to generate a migration when I don't have a DB in sync (up to the latest migration, in fact, have no DB at all) and have already made substantial changes to my model.</p>
  
  <p>This are the specific details:</p>
  
  <ol>
  <li>Have a sequence of explicit migrations.</li>
  <li>Have no database. In short, have lots of pending changes.</li>
  <li>Made changes to the models/context.</li>
  <li>When trying to Add-Migration, it will complain saying precisely that <strong>explicit migrations are pending</strong>.</li>
  <li>If I try to execute the migration (and bring my DB in sync), either via Update-Database or migrate.exe, it will fail (after applying explicit migrations successfully), <strong>and automatic migrations are not enabled.</strong></li>
  <li><strong>I don't want to enable automatic migrations either</strong> (to prevent any schema changes to be committed and go unaccounted in code.)</li>
  </ol>
  
  <p>I realize that after the failure in #5 I can now run #4. Then re-try #5 and voilá.</p>
  
  <p>My Question is if this is the expected approach to solve this silly situation.</p>