Fix #256 - let parent algorithm detect non textual selectors and deal appropriately
Adding UseCacheDependencies property to IFileReader so that HttpCache can use that to determine if it should create file cache dependencies or not. This fixes issue #245 where file cache dependencies were not working for VirtualFileReader when the virtual files mapped to embedded resources.
FIX: don't modify the HTTP Vary header if dotless is not handling the encoding
Use file exists instead of getting file. fixes #262