Fix various 20141120 (for PortForwardManager)

This is currently for review only, and for sharing with @Nakomis
I'm happy with the first two commits; but not the "TODO Hack" commit!
Yeah; not particularly happy with that.
But it means we can use a location spec of `portForwardManager(scope=global)` rather than having to do `portForwardManager(brooklyn.portForwardManager.scope=global)`. 

Also, the config being read by the `PortForwardManagerLocationResolver` doesn't respect `@SetFromFlag("scope")`. I guess that could look up the explicit string "scope" rather than referencing the config key for the lookup, but that doesn't feel good either.