A test for issue #1140
Maintain keep-alive for replies without body. Fix #1140

Cherokee closed the keep-alive connection for 204 No Content and
304 Not Modified replies. As you may understand especially the latter
has a serious performance implication in real life situation. This patch
addresses that.
Merge pull request #1143 from cherokee/1140_maintain_keepalive

Maintain keep-alive with 204 and 304 replies