Pulse driver: Fix sign error in overflow check
sound-pulse: Implement reconnect on buffer flush request

Disconnecting will cause the sink buffer to be rewound, resulting in much
lower flush latency.
sound-pulse: Allow configuring output latency.

Set default playback latency to maximum.
Set recording latency to hard-coded 100 ms for VU meter/statistics.
sound-pulse: Add prefs dialog for configuring latency
sound-pulse: Set stopping flag when stopping input to block callback