Account for Spaces OG's privacy override on preset change.

Spaces OG has special functionality in spaces_og_nodeapi() that detects when the space preset changes, and makes sure all nodes in the space follow the group privacy of the preset.

This is fine behavior for public → private settings, OG Privacy prioritizes anything making a node more private.

For private → public this results in making nodes public without regarding for OG Privacy policies.

OG Privacy needs to duplicate the Spaces preset change-check and replace the og_privacy setting of each node based on active policies.

Doing so requires a full node_load() on each node, making it a bit expensive. This should probably use Batch API.