Based on this excellent post I came up with the following instructions for upgrading from JSTL 1.1.

1. Update URI in JSP pages to use JSTL 1.1.

   <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

2. Install in WEB-INF/lib the two JSTL 1.1 jars, standard.jar and jstl.jar.  You can get these from The Jakarta Site – Standard 1.1 Taglib Downloads.
3. Update the start of web.xml to look like this.