Prevent global settings from being accidentally overwritten

On a number of occasions, upgrading Extranet has triggered some kind of bug that has caused the global settings to be reset to their default values. The most obvious cause of this is that some piece of code has created a new Settings() object and saved it through the settings manager.

One way to prevent this from happening would be to make it impossible to save a Settings object that was not first loaded from the settings manager. Have the manager 'tag' each settings object on the way through and refuse to save any that is was not responsible for loading.

Obviously there's one point where it would be necessary to create a new settings object - during initial setup - but that could be taken care of by an explicit method for that purpose.