title: C# multitarget platform dll
body: <p>I have problem with using C# dll on 3.5 and 4.5 platform. I have main app (unmanaged code) which use C# dll. And i need to target my dll to both 3.5 and 4.5 platforms.
  For C# exe application i've used app.exe.config file like</p>
  
  <pre><code>&lt;?xml version="1.0"?&gt;
  &lt;configuration&gt;
    &lt;startup&gt;
      &lt;supportedRuntime version="v2.0.50727" /&gt;
      &lt;supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0,Profile=Client"/&gt;
    &lt;/startup&gt;
  &lt;/configuration&gt;
  </code></pre>
  
  <p>I've tried to put it in dll folder, in main app folder with lib_name.config.dll and main_app.config.exe name. But it still doesn't work.
  I should target single dll to both platform (so i can't use only 3.5 or 4.5 framework).
  How can i use config file for dll?</p>