title: Unity not finding DLL dependency of another DLL (both in Assets folder)
body: <p>Background info (might be relevant):</p>
  
  <ul>
  <li>Using Unity 2017.2 with "Scripting Runtime Version" set to "Experimental (.NET 4.6 equivalent)"</li>
  <li>Writing code in Visual Studio 2017 (not MonoDevelop)</li>
  </ul>
  
  <p>I have a Unity project that makes direct use of a third-party DLL ("library A"), which I've added to the project's Assets folder. Library A depends on another DLL, "library B", which I've also added to the Assets folder. Library B is not used by any scripts in the Unity project. Both libraries A and B are written in C# and target .NET 4, i.e., they're both managed code.</p>
  
  <p>Once added to the Assets folder, both libraries A and B are listed under "References" when the project is opened in Visual Studio and "Copy Local" is set to "True" for both (although I don't know if Unity uses that property).</p>
  
  <p>However, when running the project in the Unity editor, various calls to library A raise exceptions that indicate that library B isn't available. The only way I've been able to get it to work is by placing a copy of library B in <code>C:\Program Files\Unity\Editor</code> (the directory containing Unity.exe, the Unity editor executable).</p>
  
  <p>I've used libraries A and B in other, non-Unity projects and never had any issues (Visual Studio copies them both to the output directory as long as they're referenced). Am I missing a Unity-specific step that's necessary to tell it that library B is required?</p>