Fix http://issues.apache.org/bugzilla/show_bug.cgi?id=56581
If an error on a JSP page occurs when response have already been committed,
do not clear the buffer of JspWriter, but flush it.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1600899 13f79535-47bb-0310-9956-ffa450edef68