title: Unhandled exception: System.IO.IOException: The process cannot access the file 'xxx.nupkg' because it is being used by another process
body: <p>I am trying to use squirrel for windows <em>(version 1.0.0.0)</em> and there is no way to get rid of that error.</p>
  
  <p>I have done everything to be sure that file is, indeed, not in use.</p>
  
  <p>The following steps reproduce the error on my PC. </p>
  
  <ol>
  <li>Create the nuget package to <code>releasify</code></li>
  <li>Restart the PC </li>
  <li>Open command prompt only (no other application is running, not even visual studio)</li>
  <li>Run the command <code>squirrel --releasify Digger.1.0.0.1.nupkg</code></li>
  </ol>
  
  <p>The weird thing is that I am be able to delete the file right after getting the error from the <code>releasify</code> command:</p>
  
  <p>The following is the log.</p>
  
  <pre><code>2015-08-30 17:28:03&gt; Program: Starting Squirrel Updater: --releasify Digger.1.0.0.1.nupkg
  2015-08-30 17:28:03&gt; Program: Bootstrapper EXE found at:C:\dev\utils\squirrel\Setup.exe
  2015-08-30 17:28:03&gt; Program: Creating release package: C:\dev\projects\ThirdParty\inmediati\Digger\Digger.Cliente.WPF\Releases\Digger.1.0.0.1.nupkg
  2015-08-30 17:28:03&gt; ReleasePackage: Creating release package: C:\dev\projects\ThirdParty\inmediati\Digger\Digger.Cliente.WPF\Releases\Digger.1.0.0.1.nupkg =&gt; C:\dev\projects\ThirdParty\inmediati\Digger\Digger.Cliente.WPF\Releases\Digger-1.0.0.1-full.nupkg
  2015-08-30 17:28:03&gt; ReleasePackage: Extracting dependent packages: []
  2015-08-30 17:28:03&gt; ReleasePackage: Removing unnecessary data
  2015-08-30 17:28:03&gt; ReleasePackage: No release notes found in C:\Users\Juan\AppData\Local\SquirrelTemp\tempa\Digger.nuspec
  2015-08-30 17:28:03&gt; Unhandled exception: System.IO.IOException: The process cannot access the file 'C:\dev\projects\ThirdParty\inmediati\Digger\Digger.Cliente.WPF\Releases\Digger.1.0.0.1.nupkg' because it is being used by another process.
     at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
     at System.IO.File.InternalDelete(String path, Boolean checkHost)
     at System.IO.File.Delete(String path)
     at Squirrel.Update.Program.Releasify(String package, String targetDir, String packagesDir, String bootstrapperExe, String backgroundGif, String signingOpts, String baseUrl, String setupIcon)
     at Squirrel.Update.Program.executeCommandLine(String[] args)
     at Squirrel.Update.Program.main(String[] args)
  </code></pre>
  
  <p><em>BTW: The nuget package was created using a <code>Any CPU</code> build.</em></p>