Upgrade projects to VS 2013.
Add NSass/libsass as a processor for SASS:
  Remove SassProcessor from Global.asax because it makes testing the
  NSassProcessor impossible.
  AutoBundling tests for SASS are broken because the handler is no longer
  registered - will need to work this out with Alex Cuse.
force inclusion of nsasstest.scss (blocked by .gitignore previously)