Reduce the base latencies for capture and playback by half a period,
and let the update method account for the additional playback latency
introduced by OSS buffer management.
This fits actual OSS latencies better, so the same settings for the
extra input-latency and output-latency parameters should apply to
different period lengths.
Beware that this change invalidates current input-latency and
output-latency values, they have to be measured again.
Features:
* Internal workings more in line with other Jack drivers.
* Use poll() for wait and sync instead of blocking I/O.
* Allows to use Jack in "async" mode.
* Calculate DSP usage correctly.
* OSS buffer management to achieve stable latencies.
* Latency correction for asymmetric OSS buffer use.
* More robust handling of over- and underruns.
* Handle format changes forced by the OSS interface.
* FreeBSD 24bit samples are always packed.
No changes to the driver parameters or the user interface.