Add operations to insert and delete map infos from an AG_fs_map
Implement stable driver API methods to request that the AG publish or
delete a file/directory.  This allows the driver to listen to the
underlying data repository and propagate changes to Syndicate.
Implement AG_fs_publish and AG_fs_delete, to be called to publish/delete
single files/directories synchronously.
Tweak the workqueue API for publish/delete operations, so the driver
supplies the map_info structure on publish but only the path on delete.