MYFACES-3695 'Cannot set header. Response already committed.' on WebSphere Application Server 7 and 8 (do not write header if response was already committed)

git-svn-id: https://svn.apache.org/repos/asf/myfaces/core/branches/2.0.x@1461884 13f79535-47bb-0310-9956-ffa450edef68