Memory limited job runner

This is another component needed for the new splitfile code (db4o purge).
Fix what about this? Not being a direct argument? Why isn't it?

This argument is huge - any thoughts on improving the readability, like in [OfficialPlugins](https://github.com/freenet/fred-staging/blob/next/src/freenet/pluginmanager/OfficialPlugins.java#L23), or some kind of argument struct?