Improved 50x error page.
Improved 50x error page.

The feature set of the new page:

 - HTML5 compliant;
 - Looks similar to the new "Welcome page" (r4835);
 - Sysadmin hint with a link to the documentation of the "error_log" directive.

hy0kl/nginx,hy0kl/nginx,firebase/nginx,firebase/nginx,hy0kl/nginx,firebase/nginx,firebase/nginx