Can't specify location of web.xml

When the WAR plugin was converted from using Ant's <war> task to using the <jar> task we lost the ability to use the ${maven.war.webxml} property to specify the location of the web.xml file. Not only does this reduce flexibility (the only place you can put web.xml is in ${maven.war.src}/WEB-INF/web.xml), but it prevents the token filtering tip (in xdocs/tips.xml) from working.