If we have a pending command, then the player thread is already awake.
Even if not, we'll wake it up as soon as we have finished the command.

Simplify the code, eliminate duplicate rollback code and eliminate the
"goto" kludge.

Now that I can see the Reopen() method clearly, it is obvious that the
out_audio_format setting will get overwritten by the following Open()
call.

Now that CloseFilter() may be called again, we can reduce code
duplication.

This allows calling CloseFilter() multiple times.

For easier state management inside filter plugins.

This only applies to linux systems.  Here, sched_setscheduler() is
called to get realtime scheduling.  With this patch, the return value
of this function is now checked and a warning / error message is
generated if it fails.

Works around the "PCM conversion from f to dsd is not implemented"
error message that prevents DSD playback.

Fixes memory leak because ao_plugin_close() never gets called.

Be consistent.