By using the firebug add-on in firefox, we can see that there are unnecessary http requests for the static resources of the disk usage plugin.

For example, for every display of the home page https://builds.apache.org/
there is unnecessary http request for diskusage48.png (see "jenkins home page.png"). The browser should know that this is useless to ask.

According to https://groups.google.com/forum/#!msg/jenkinsci-dev/qQf7Tuu6uiw/_WO7OBj_LIkJ
this can be fixed by using "Jenkins.getResourcePath()" or ${resURL}.

Firebug can be used locally to check the changes.