Re-added internal class generated for AssemblyInfo.vb

Was removed in 63185e7 for #673 due to
errors building. The existing code did not work because of the attempt
to put it in the System namespace, and the lack of a class name.

src/app/FakeLib/AssemblyInfoFile.fs

@@ -181,7 +181,14 @@ let CreateVisualBasicAssemblyInfoWithConfig outputFileName attributes (config :
              |> Seq.toList
              |> List.map (fun (attr : Attribute) -> sprintf "<assembly: %sAttribute(%s)>" attr.Name attr.Value))
 
-    attributeLines 
+    let sourceLines =
+        if generateClass then
+            [ "Friend NotInheritable Class AssemblyVersionInformation"
+              sprintf "    Friend Const Version As String = %s" (getAssemblyVersionInfo attributes)
+              "End Class" ]
+        else []
+
+    attributeLines @ sourceLines
     |> writeToFile outputFileName
     traceEndTask "AssemblyInfo" outputFileName