Make Zone.CreateFromUrl() work with URLs like file://C:\foo\bar

Make Zone.CreateFromUrl() work with URLs like file://C:\foo\bar

On Windows the test used URLs like `file://C:\tmp\foo` which the
Mono.Security.Uri class was incapable of parsing. System.Uri from
referencesource parses such URLs just fine. This patch fixes the Uri class to
be able to parse such URLs. It also changes the Zone class to not throw an
exception if the Zone.CreateFromUrl() method is passed an invalid URL. Instead
the zone is set to NoZone. This seems to be how Zone in .NET behaves.