Maven2 modules should have an option to monitor updates of dependencies as build
trigger. Currently only modules that build in the same hudson-instance are able
to trigger a rebuild of downstream modules. It could be usefull to have a
rebuild triggered by a new version of any dependency.

URL monitor as suggested in issue 744 could be used to implement this.

Dependencies could be collected from the previous build. They don't change that
often, and, if SCM build trigging is used as well, committed updates of
dependencies in pom.xml would normally trigger a build anyway.