The MirDisplayConfiguration returned on the client can be incorrect

Assume that a client has the active surface and reconfigures the display.

The server receives a configure_display() request, queues a change to be executed on the main loop, and returns the current active display configuration.

Note that it *does not* wait for the main loop to service the change request so the active configuration can be the one prior to the change.

The client caches this configuration and will return it from mir_connection_create_display_config().

One might hope the client would get a notification via mir_connection_set_display_config_change_callback() when the config is actually updated, but that doesn't happen.