Added dynamic wrapper support to IFileSystem to allow context specific implementations from which to hang extension methods upon (ie IMediaFileSystem)

src/Umbraco.Core/IO/IFileSystem.cs

@@ -29,6 +29,7 @@ namespace Umbraco.Core.IO
 
         bool FileExists(string path);
 
+
         string GetRelativePath(string fullPathOrUrl);
 
         string GetFullPath(string path);