fix 204 codes parsing

Sometimes when say riak returns 204 code ibrowse returns response in tuple of different size holding request body itself, like this:

``` erlang
{:ok, '204', 
	[{'Vary', 'Accept-Encoding'}, 
	 {'Server', 'MochiWeb/1.1 WebMachine/1.9.2 (someone had painted it blue)'}, 
	 {'Date', 'Mon, 17 Mar 2014 10:32:53 GMT'}, 
	 {'Content-Type', 'application/json'}, 
	 {'Content-Length', '0'}
	], 
	[], 
	"DELETE /riak/testbucket/ek0qjcmndjosushea0gh19olp6 HTTP/1.1\r\nHost: 127.0.0.1:8098\r\nContent-Length: 0\r\n\r\n"
```