Do not wait for body, if it is skipped explicitly.

Hello, Martin,

First of all, thank you for a useful gem.

I've added support for `:max_chunks => 0`, so now one can easily test those actions, that render nothing on connection (currently a timeout exception is being raised), e. g.

```ruby
it 'should establish connection' do
  get('/sse', :max_chunks => 0).should respond_with :status => :ok
end
```