Don't create RollupRules until necessary

OpenJDK7 installed from FreeBSD ports has lack of built-in Javascript ScriptEngine support and
could not be used for running selenese-runner-java due to the NullPointerException.
(I don't test but OpenJDK7 in OpenBSD and DragonflyBSD ports seem to have the same problem)

This PR is a simple workaround for above problem