Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- Increase dynamic range of filter coefficients from 28bit to 30bit.
This cause dramatic effect in overall precision and conversion quality
by pushing down most aliasing artifacts around -180 dB.

Spectrogram analysis/comparison:

http://people.freebsd.org/~ariff/z_comparison/z_28vs30/

- Guard against possible 64bit overflow during accumulation process by
slightly normalize and saturate sample and coefficient multiplication,
possible during extreme 32bit downsampling (eg. 380KHz -> 8KHz) with
custom preset that require more than ~7000 taps filter (which is
overkill).

- Add knobs through FEEDER_RATE_PRESETS to set dynamic range of filter
coefficients/accumulator and prefered polynomial interpolator:

COEFFICIENT_BIT:X
(where 1 <= X <= 30, default: 30)

ACCUMULATOR_BIT:X
(where 32 <= X <=64, default: 58)

INTERPOLATOR:I
(where I = ZOH, LINEAR, QUADRATIC, HERMITE, BSPLINE,
OPT32X, OPT16X, OPT8X, OPT4X, OPT2X)

Approved by: re (kib)

Slightly increase amount of bandwidth of resampling filter for
feeder_rate_quality=3. This have the benefit of reducing aliasing
artifacts due to alias masking.

Spectrogram analysis:

o Old preset (100:36:0.90)
http://people.freebsd.org/~ariff/z_comparison/z_q3_old.png

o New preset (100:36:0.92):
http://people.freebsd.org/~ariff/z_comparison/z_q3_new.png

Approved by: re (kib)

- Add a way to change filter oversampling factor through
FEEDER_RATE_PRESET "OVERSAMPLING_FACTOR:X .. .." where
X = log2(oversampling factor).

- Lower down default filter oversampling factor from 128
(log2 = 7) to 32 (log2 = 5), saving worth of 80 Kb.
The use of better polynomial interpolator will raise
its conversion quality/accuracy to match (or slightly
better) with previous settings.

- Bump driver version.

Move all sound related scripts to its own 'sound' subdir.

Suggested by: jmallett