Use clock_gettime instead of portaudio timing.

Pa_GetStreamTime on Ubuntu 10.04 always returns 0. On FreeBSD,
it can return the same value couple of times in a row:

185.7596
185.7596
185.7596
232.1995
232.1995
232.1995
278.6395
278.6395
325.0794
325.0794
325.0794
325.0794

This lowers the framerate, effectively disabling picture zooming
effect, since the effect lasts only a brief period.

If PA_TIMING_FIX is defined, clock_gettime will be used instead
of PortAudio timing. It should provide a monotonic clock.
dedicated timing functions for macosx and linux

Using CLOCK_MONOTONIC on unix and mach timers on osx.
debug symbols activated in debug builds
use latency information when running under PA_TIMING_FIX
Merge branch 'F-FixTimingIssues'

* F-FixTimingIssues:
  use latency information when running under PA_TIMING_FIX
  debug symbols activated in debug builds
  dedicated timing functions for macosx and linux
  Use clock_gettime instead of portaudio timing.