All backends are expected to support the exact argument. A friendly log message
will be printed to prompt users to upgrade backends that fail due to this.
While trying to remove traces of stop calls in core to get gapless working I
found we had no way to switch to switch tracks without triggering a play. This
change fixes this by changing the backends playback provider API.
- play() now _only_ starts playback and does not take any arguments.
- prepare_change() has been added, this could have been avoided with a kwarg to
change_track(track), but that would break more backends.
- core has been updated to call prepare_change+change_track+play as needed.
- tests have been updated to handle this change.
Longer term I hope to completely rework the playback API in backends, as 99% of
our backends only use change_track(track) to translate URIs. So we should make
simple case simple, and handle mopidy-spotify / appsrc in some other way.
Cherry picked from the WIP gapless branch.
The default was insane. For one, because overriding e.g. just the
getter would make the property have a pair of working getter and
setter that are entirely disconnected.
