BufferedResponseWrapper implementation does not adhere to servlet specs regarding content type setting

org.displaytag.filter.BufferedResponseWrapper13Impl.setCharacterEncoding(String) stupidly sets the content type without handling the char encoding correct. The specs of javax.servlet.ServletResponse.setContentType(String) clearly says:
{quote}
* Sets the content type of the response being sent to
     * the client, if the response has not been committed yet.
     * The given content type may include a character encoding
     * specification, for example, <code>text/html;charset=UTF-8</code>.
     * The response's character encoding is only set from the given
     * content type if this method is called before <code>getWriter</code>
     * is called.
     * <p>This method may be called repeatedly to change content type and
     * character encoding.
     * This method has no effect if called after the response
     * has been committed. It does not set the response's character
     * encoding if it is called after <code>getWriter</code>
     * has been called or after the response has been committed.
     * <p>Containers must communicate the content type and the character
     * encoding used for the servlet response's writer to the client if
     * the protocol provides a way for doing so. In the case of HTTP,
     * the <code>Content-Type</code> header is used.
{quote}

Tomcat's repsonse implementation does this clearly. This impl does not. I have patched the issue. Now it works as specified. This one is related to DISPL-471.