One bug I noticed in LauchDownload.isUpdateAvailable() is that it goes
only one level down to extensions from the main app jnlp. If an
extension has updated extensions, they won't be checked. All jars
(included in all extensions) are checked though.
a.jnlp -> b.jnlp (component ext) -> c.jnlp (component ext)
there is no update check for c.jnlp