Document that redirect feature for not-found pages might not work in older appservers

Re: CONF-8766, the Confluence feature that redirects users to pages that have been moved or had their name truncated in the URL may not work on servers that only support the Servlet 2.3 specification, such as Tomcat 5.0. It will work fine with any application server that fully supports the Servlet specification v2.4 or higher, or the J2EE specification v1.4 or higher.

Applications that (claim to) support Servlet 2.4 or J2EE 1.4 include:

• Websphere 6.1
• Weblogic 9
• Tomcat 5.5
• Resin 3.0

We should document this alongside any documentation of the feature itself, and possibly put a caveat in the system requirements stating that while Servlet 2.3 is a supported platform, some functionality may be degraded in older application servers.