Changes

Summary

1. recover Url.is_wellformed from before d8330439823a, e.g. relevant for JEdit_Resources.read_file_content (the URI alone does not necessarily have a protocol prefix, so plain file-path would be treated as URL);
2. proper php-fpm configuration for nginx;
3. support multiple webservers: Apache or Nginx;
4. tuned;
5. clarified signature: explicit type isabelle.Url to avoid oddities of java.net.URL (e.g. its "equals" method);
6. unused;