title: Can not find system.web.http
body: <p>I have to add a system.web.http assembly reference because I added the HttpConfiguration class to my unit test class library project.</p>
  
  <p>When I browse the Add reference dialog I can not find the system.web.http assembly.</p>
  
  <p>The class library project has the .Net 4.5.1 framework targeted.</p>