reverted back to old FFT

Da's new FHT was licensed under the non-permissive GPL, and also
had some problems when BUF_SIZE was increased past 512. Note that
at this point we're still using the built-in complex type rather
than the custom-defined one that was being used earlier.
replaced barrier with pthread_join

This fixed the issue with playback with > 2 objects on the physical
device, where tons of threads were being created and not destroyed.
It also avoids the dependency on the custom barrier class, though is
it the best (fastest) solution? I'm still a little unsure on the
differences between pthread_joins and barriers...
added some test graphs/data