title: EF Update current migration file instead of create a new one
body: <p>I know it's against the purpose of migration, but it doesn't make sense to me to make a new migration file for every single changes that I do to the model. </p>
  
  <p>I start with enabling migration, then initial the migration and visual studio make a <code>201502151515_initial.cs</code></p>
  
  <p>i do some changes in the 201502151515_initial.cs file and go for update-database.</p>
  
  <p>then I understand I have some bug in the  model. 
  then if i try to <code>update-database</code> it will fail and show me this error: </p>
  
  <blockquote>
    <p>Unable to update database to match the current model because there are
    pending changes and automatic migration is disabled. Either write the
    pending model changes to a code-based migration or enable automatic
    migration. Set DbMigrationsConfiguration.AutomaticMigrationsEnabled to
    true to enable automatic migration. You can use the Add-Migration
    command to write the pending model changes to a code-based migration.</p>
  </blockquote>
  
  <p>if I try to add-migration, then it will create another file for me</p>
  
  <p>is it anyway to update the current <code>201502151515_initial.cs</code> file?</p>
  
  <p>I can do it manually that is a hell of task to make sure everything is fine. 
  I can delete the current file and create it again, in this case i have inconsistency with database(because I already update-database).
  or find a better way to update the current file.</p>
  
  <p>is it any better way to do it?</p>