Fix integration tests for Net HTTP Server.

This fixes #670. 

Unfortunately, seems like `parslet` (a `net-http-server` dependency) is broken, which causes `starts the correct server` test to fail. 

The problem is that when running:

```
RACK_ENV=development exec "/Users/patricio/.rbenv/versions/1.9.3-p392/bin/ruby" -w -I "/Users/patricio/Code/github/sinatra/lib" "/Users/patricio/Code/github/sinatra/test/integration/app.rb" -s HTTP -o 127.0.0.1 -p 5002 -e development 2>&1
```

(generated by https://github.com/sinatra/sinatra/blob/master/test/integration_helper.rb#L96)

parslet crashes:

```
loading
starting
/Users/patricio/.rbenv/versions/1.9.3-p392/lib/ruby/gems/1.9.1/gems/net-http-server-0.2.2/lib/net/http/server/daemon.rb:109: warning: assigned but unused variable - error
/Users/patricio/.rbenv/versions/1.9.3-p392/lib/ruby/gems/1.9.1/gems/parslet-1.5.0/lib/parslet/source/line_cache.rb:42: warning: `-' after local variable is interpreted as binary operator
/Users/patricio/.rbenv/versions/1.9.3-p392/lib/ruby/gems/1.9.1/gems/parslet-1.5.0/lib/parslet/source/line_cache.rb:42: warning: even though it seems like unary operator
/Users/patricio/.rbenv/versions/1.9.3-p392/lib/ruby/gems/1.9.1/gems/parslet-1.5.0/lib/parslet/atoms/base.rb:83: warning: assigned but unused variable - value
/Users/patricio/.rbenv/versions/1.9.3-p392/lib/ruby/gems/1.9.1/gems/parslet-1.5.0/lib/parslet/atoms/lookahead.rb:27: warning: assigned but unused variable - value
/Users/patricio/.rbenv/versions/1.9.3-p392/lib/ruby/gems/1.9.1/gems/parslet-1.5.0/lib/parslet/error_reporter/deepest.rb:62: warning: assigned but unused variable - rank
/Users/patricio/.rbenv/versions/1.9.3-p392/lib/ruby/gems/1.9.1/gems/net-http-server-0.2.2/lib/net/http/server/chunked_stream.rb:51: warning: assigned but unused variable - chunk_extension
```