adjust amused-monitor not to query amused on certain events but use the new extra info that `amused monitor' prints.

The monitor mode now has access to some additional information other than just the name of the event. The `mode' and `seek' events now report the mode status and the position/duration respectively, allowing consumers of `amused monitor' to show correct and coherent information. It helps in particular applications like `amused-monitor' (in contrib/) that show a progress bar for the current song. Before, they had to run their own timers and periodically synchronize using `amused status', now they can just update the state in the same `amused-monitor' event loop.

First move towards a change in the behaviour of `monitor': advancement on tracks during the play are reported also every second, as the music is played, not only when there's an explicit seek.