SAL UpgradeTask framework doesn't work in Stash

There are two issues with SAL PluginUpgradeManager deployed in Stash.

1. It is not exposed via OSGi as LifecycleAware, so it's onStart() method is never called (so upgrades are not triggered on startup).
2. It implements DisposableBean and InitializingBean, but afterPropertiesSet() and destroy() are also not called. This due to the fact that sal-core is exported from the host application which is using Spring 3.x, so the plugin system (using Spring 2.x) doesn't recognise the versions of DisposableBean and InitializingBean when it does it's "assignable from" comparison.