Update tests to use the official xunit
Handle wrapped exceptions in Database Error Page
If a database exception is wrapped later in the request (after EF has logged it) then we were not displaying the database error page.
This was occurring in ASP.NET Identity where the exception was getting wrapped in an AggregateException.
We now walk the tree of inner exceptions looking for a match.
Also adding some extra logging as this was hard to debug without resorting to source code.