Find a way to allow users to store the game world with version control

[mike]

This is fairly open ended, but for a game studio to want to use MV3D, they'll want to be able to keep a version history of the world. This may include looking into the current datastore mechanism and possibly considering major changes there.

This is likely also related to instancing because instances will have some state that won't exist in MV3D until needed, and multiple copies of that state will be made.

[mike]

First pass at v0.42 planning.

[mike]

Should be able to just design and implement a way to use a SQLiteStore to freeze and unfreeze areas. When freezing, object ids are freed. When unfreezing, new oids are created. This should permit multiple copies of the same data to be loaded.

This requires the sim service to be converted to use the new persist service.

[mike]

Created branch /branches/374-savegame.

[mike]

Fixed in [1027]. See /trunk/mv3d/test/service/test_persistservice TestFreezer? for examples of use.