Enable zero-copy deployment of WARs into Jetty

Similar to Tomcat, Jetty 6.x onwards can be configured to run a web application from an arbitrary directory, i.e. there's no need to copy the actual WAR into a folder within the server home. The attached patch enhances the already created context files to simply point at the orignal location of the WAR instead of copying it to the webapps directory and reference that copy.