title: EF6 re-scaffold initial migration
body: <p>Please help me with one inconvenience in ef6 migrations.
  I change my model very often(because I don't have complete understanding of schema).
  I have two migration:
  1. Initial (ef6 generates this migration by my model)
  2. AddtionalInit (some manual sql code that need to be executed after initialization)</p>
  
  <p>When I change my model I want to re-scaffold Initial migration to apply changes. I migrate to -TargetMigration:0 and try to execute:</p>
  
  <pre><code>add-migration Initial -force
  </code></pre>
  
  <p>but it throw with error</p>
  
  <pre><code>Unable to generate an explicit migration because the following explicit migrations are pending: [201709290630180_Initial, 201709290631135_AdditionalInit]. Apply the pending explicit migrations before attempting to generate a new explicit migration
  </code></pre>
  
  <p>Can I re-scaffold Initial migration without deleting AdditionalInit migration?</p>
  
  <p>P.S. Sorry for English. </p>