Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56555
When Tomcat closes the connection based on the HTTP status code of the response, ensure that only one connection header is sent to the client.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1598007 13f79535-47bb-0310-9956-ffa450edef68