When a preference panel is opened, the prefs panel makes a clone of the current SettingsManager for a scratch pad. When the window is closed, these clones are never freed. The reason for this is because each SettingsManager instance adds an event to EventManager: every 30 seconds the SettingsManager should be saved. This will hold the reference to the clone alive indefinately causing (eventually) a memory leak. There are a few possible solutions to this:
* Weak reference event manager - an object can add a function and, in the event manager, only a weak reference will be kept. This seems to be the best if not just for completeness in the event manager.
* SettingsManagers will not add a tick event if there is no location to save to (clones will have their 'loc' property set to None)
* dereference events explicitly, OK and Cancel callbacks for the preference pane will call a destroy() on settings as necessary.
Steps to reproduce:
1. check out trunk -r 1868
2. apply attached patch
3. run exaile in terminal
4. while bored or not satisfied:
i. open preferences
ii. close preferences
5. note in the console saves are still being called for preference panes 1..n (0 is the main one for exaile)
we really should make the event system use weakrefs instead of normal refs, then things like this couldn't happen.