puma/puma — pull request #470 by arthurnn (2014-02-17 17:11:33+00:00)
Title: Add config to customize the default error message

Add a `lowlevel_error_handler`, so we can customize the default error message.

example:

```ruby
lowlevel_error_handler do
[302, {'Content-Type' => 'text', 'Location' => 'foo.html'}, ['302 found']]
end
```

[fix #458]