title: I get "Assembly outside lib folder" warning when assembly is actually inside the lib
body: <p>Here's the error I get:</p>
  
  <pre><code>&gt;./NuGet.exe pack MyAssembly.nuspec
  Attempting to build package from 'MyAssembly.nuspec'.
  Successfully created package 'V:\...\MyAssembly\bin\Publish\MyAssembly.0.0.0.nupkg'.
  WARNING: Issue found with package 'MyAssembly'.
  
  WARNING: Issue: Assembly outside lib folder.
  WARNING: Description: The assembly 'lib/net46/MyAssembly.dll' is not inside the 'lib' folder and hence it won't be added as reference when the package is installed into a project.
  WARNING: Solution: Move it into the 'lib' folder if it should be referenced.
  </code></pre>
  
  <p>And here's include I use:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;package&gt;
    &lt;metadata&gt;
      &lt;id&gt;MyAssembly&lt;/id&gt;
      &lt;version&gt;0.0.0&lt;/version&gt;
      &lt;authors&gt;Poma&lt;/authors&gt;
      &lt;description&gt;MyAssembly&lt;/description&gt;
    &lt;/metadata&gt;
    &lt;files&gt;
      &lt;file src="MyAssembly.dll" target="lib/net46/" /&gt;
    &lt;/files&gt;
  &lt;/package&gt;
  </code></pre>
  
  <p>I checked with NuGet Explorer and dll is indeed in lib/net46. What could be wrong here?</p>
  
  <p><strong>Update:</strong> this happens with NuGet 3.5 and 4.1 but doesn't happen with 3.4</p>